tighten up array handling, fix bug with array_slice output type inference (#12914)

core/src/main/java/org/apache/druid/math/expr/ApplyFunction.java

@@ -407,7 +407,7 @@ public interface ApplyFunction
         return ExprEval.of(null);
       }
       if (hadEmpty) {
-        return ExprEval.ofStringArray(new String[0]);
+        return ExprEval.ofStringArray(new Object[0]);
       }
       Expr accExpr = argsExpr.get(argsExpr.size() - 1);
 
@@ -576,9 +576,12 @@ public interface ApplyFunction
     @Override
     public ExprEval match(Object[] values, LambdaExpr expr, SettableLambdaBinding bindings)
     {
-      boolean anyMatch = Arrays.stream(values)
+      for (Object o : values) {
-                               .anyMatch(o -> expr.eval(bindings.withBinding(expr.getIdentifier(), o)).asBoolean());
+        if (expr.eval(bindings.withBinding(expr.getIdentifier(), o)).asBoolean()) {
-      return ExprEval.ofLongBoolean(anyMatch);
+          return ExprEval.ofLongBoolean(true);
+        }
+      }
+      return ExprEval.ofLongBoolean(false);
     }
   }
 
@@ -599,9 +602,12 @@ public interface ApplyFunction
     @Override
     public ExprEval match(Object[] values, LambdaExpr expr, SettableLambdaBinding bindings)
     {
-      boolean allMatch = Arrays.stream(values)
+      for (Object o : values) {
-                               .allMatch(o -> expr.eval(bindings.withBinding(expr.getIdentifier(), o)).asBoolean());
+        if (!expr.eval(bindings.withBinding(expr.getIdentifier(), o)).asBoolean()) {
-      return ExprEval.ofLongBoolean(allMatch);
+          return ExprEval.ofLongBoolean(false);
+        }
+      }
+      return ExprEval.ofLongBoolean(true);
     }
   }
 

core/src/main/java/org/apache/druid/math/expr/Evals.java

@@ -20,7 +20,6 @@
 package org.apache.druid.math.expr;
 
 import org.apache.druid.common.config.NullHandling;
-import org.apache.druid.java.util.common.logger.Logger;
 
 import javax.annotation.Nullable;
 import java.util.Arrays;
@@ -30,8 +29,6 @@ import java.util.List;
  */
 public class Evals
 {
-  private static final Logger log = new Logger(Evals.class);
-
   public static boolean isAllConstants(Expr... exprs)
   {
     return isAllConstants(Arrays.asList(exprs));
@@ -71,4 +68,16 @@ public class Evals
   {
     return !NullHandling.isNullOrEquivalent(x) && Boolean.parseBoolean(x);
   }
+
+  /**
+   * Call {@link Object#toString()} on a non-null value
+   */
+  @Nullable
+  public static String asString(@Nullable Object o)
+  {
+    if (o == null) {
+      return null;
+    }
+    return o.toString();
+  }
 }

core/src/main/java/org/apache/druid/math/expr/ExprEval.java

@@ -161,22 +161,28 @@ public abstract class ExprEval<T>
       }
 
       if (coercedType == Long.class || coercedType == Integer.class) {
-        return new NonnullPair<>(
+        Object[] array = new Object[val.size()];
-            ExpressionType.LONG_ARRAY,
+        int i = 0;
-            val.stream().map(x -> x != null ? ExprEval.ofType(ExpressionType.LONG, x).value() : null).toArray()
+        for (Object o : val) {
-        );
+          array[i++] = o == null ? null : ExprEval.ofType(ExpressionType.LONG, o).value();
+        }
+        return new NonnullPair<>(ExpressionType.LONG_ARRAY, array);
       }
       if (coercedType == Float.class || coercedType == Double.class) {
-        return new NonnullPair<>(
+        Object[] array = new Object[val.size()];
-            ExpressionType.DOUBLE_ARRAY,
+        int i = 0;
-            val.stream().map(x -> x != null ? ExprEval.ofType(ExpressionType.DOUBLE, x).value() : null).toArray()
+        for (Object o : val) {
-        );
+          array[i++] = o == null ? null : ExprEval.ofType(ExpressionType.DOUBLE, o).value();
+        }
+        return new NonnullPair<>(ExpressionType.DOUBLE_ARRAY, array);
       }
       // default to string
-      return new NonnullPair<>(
+      Object[] array = new Object[val.size()];
-          ExpressionType.STRING_ARRAY,
+      int i = 0;
-          val.stream().map(x -> x != null ? ExprEval.ofType(ExpressionType.STRING, x).value() : null).toArray()
+      for (Object o : val) {
-      );
+        array[i++] = o == null ? null : ExprEval.ofType(ExpressionType.STRING, o).value();
+      }
+      return new NonnullPair<>(ExpressionType.STRING_ARRAY, array);
     }
     if (homogenizeMultiValueStrings) {
       return new NonnullPair<>(ExpressionType.STRING_ARRAY, new Object[]{null});
@@ -297,7 +303,7 @@ public abstract class ExprEval<T>
     return new DoubleExprEval(doubleValue);
   }
 
-  public static ExprEval ofLongArray(@Nullable Long[] longValue)
+  public static ExprEval ofLongArray(@Nullable Object[] longValue)
   {
     if (longValue == null) {
       return ArrayExprEval.OF_NULL_LONG;
@@ -305,7 +311,7 @@ public abstract class ExprEval<T>
     return new ArrayExprEval(ExpressionType.LONG_ARRAY, longValue);
   }
 
-  public static ExprEval ofDoubleArray(@Nullable Double[] doubleValue)
+  public static ExprEval ofDoubleArray(@Nullable Object[] doubleValue)
   {
     if (doubleValue == null) {
       return ArrayExprEval.OF_NULL_DOUBLE;
@@ -313,7 +319,7 @@ public abstract class ExprEval<T>
     return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, doubleValue);
   }
 
-  public static ExprEval ofStringArray(@Nullable String[] stringValue)
+  public static ExprEval ofStringArray(@Nullable Object[] stringValue)
   {
     if (stringValue == null) {
       return ArrayExprEval.OF_NULL_STRING;
@@ -388,16 +394,60 @@ public abstract class ExprEval<T>
       return new StringExprEval(String.valueOf(val));
     }
     if (val instanceof Long[]) {
-      return new ArrayExprEval(ExpressionType.LONG_ARRAY, (Long[]) val);
+      final Long[] inputArray = (Long[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.LONG_ARRAY, array);
+    }
+    if (val instanceof long[]) {
+      final long[] longArray = (long[]) val;
+      final Object[] array = new Object[longArray.length];
+      for (int i = 0; i < longArray.length; i++) {
+        array[i] = longArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.LONG_ARRAY, array);
     }
     if (val instanceof Double[]) {
-      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, (Double[]) val);
+      final Double[] inputArray = (Double[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, array);
+    }
+    if (val instanceof double[]) {
+      final double[] inputArray = (double[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, array);
     }
     if (val instanceof Float[]) {
-      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, Arrays.stream((Float[]) val).map(Float::doubleValue).toArray());
+      final Float[] inputArray = (Float[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i] != null ? inputArray[i].doubleValue() : null;
+      }
+      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, array);
+    }
+    if (val instanceof float[]) {
+      final float[] inputArray = (float[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.DOUBLE_ARRAY, array);
     }
     if (val instanceof String[]) {
-      return new ArrayExprEval(ExpressionType.STRING_ARRAY, (String[]) val);
+      final String[] inputArray = (String[]) val;
+      final Object[] array = new Object[inputArray.length];
+      for (int i = 0; i < inputArray.length; i++) {
+        array[i] = inputArray[i];
+      }
+      return new ArrayExprEval(ExpressionType.STRING_ARRAY, array);
     }
 
     if (val instanceof List || val instanceof Object[]) {
@@ -429,7 +479,12 @@ public abstract class ExprEval<T>
       case STRING:
         // not all who claim to be "STRING" are always a String, prepare ourselves...
         if (value instanceof String[]) {
-          return new ArrayExprEval(ExpressionType.STRING_ARRAY, (String[]) value);
+          final String[] inputArray = (String[]) value;
+          final Object[] array = new Object[inputArray.length];
+          for (int i = 0; i < inputArray.length; i++) {
+            array[i] = inputArray[i];
+          }
+          return new ArrayExprEval(ExpressionType.STRING_ARRAY, array);
         }
         if (value instanceof Object[]) {
           return bestEffortOf(value);
@@ -437,10 +492,7 @@ public abstract class ExprEval<T>
         if (value instanceof List) {
           return bestEffortOf(value);
         }
-        if (value == null) {
+        return of(Evals.asString(value));
-          return of(null);
-        }
-        return of(String.valueOf(value));
       case LONG:
         if (value instanceof Number) {
           return ofLong((Number) value);
@@ -571,12 +623,7 @@ public abstract class ExprEval<T>
   public String asString()
   {
     if (!stringValueCached) {
-      if (value == null) {
+      stringValue = Evals.asString(value);
-        stringValue = null;
-      } else {
-        stringValue = String.valueOf(value);
-      }
-
       stringValueCached = true;
     }
 
@@ -630,15 +677,6 @@ public abstract class ExprEval<T>
   @Nullable
   public abstract Object[] asArray();
 
-  @Nullable
-  public abstract String[] asStringArray();
-
-  @Nullable
-  public abstract Long[] asLongArray();
-
-  @Nullable
-  public abstract Double[] asDoubleArray();
-
   public abstract ExprEval castTo(ExpressionType castTo);
 
   public abstract Expr toExpr();
@@ -668,27 +706,6 @@ public abstract class ExprEval<T>
       return value.doubleValue();
     }
 
-    @Nullable
-    @Override
-    public String[] asStringArray()
-    {
-      return isNumericNull() ? null : new String[] {value.toString()};
-    }
-
-    @Nullable
-    @Override
-    public Long[] asLongArray()
-    {
-      return isNumericNull() ? null : new Long[] {value.longValue()};
-    }
-
-    @Nullable
-    @Override
-    public Double[] asDoubleArray()
-    {
-      return isNumericNull() ? null : new Double[] {value.doubleValue()};
-    }
-
     @Override
     public boolean isNumericNull()
     {
@@ -721,7 +738,7 @@ public abstract class ExprEval<T>
     @Override
     public Object[] asArray()
     {
-      return asDoubleArray();
+      return isNumericNull() ? null : new Object[] {value.doubleValue()};
     }
 
     @Override
@@ -741,11 +758,11 @@ public abstract class ExprEval<T>
         case ARRAY:
           switch (castTo.getElementType().getType()) {
             case DOUBLE:
-              return ExprEval.ofDoubleArray(asDoubleArray());
+              return ExprEval.ofDoubleArray(asArray());
             case LONG:
-              return ExprEval.ofLongArray(asLongArray());
+              return ExprEval.ofLongArray(value == null ? null : new Object[] {value.longValue()});
             case STRING:
-              return ExprEval.ofStringArray(asStringArray());
+              return ExprEval.ofStringArray(value == null ? null : new Object[] {value.toString()});
           }
       }
       throw new IAE("invalid type " + castTo);
@@ -786,14 +803,7 @@ public abstract class ExprEval<T>
     @Override
     public Object[] asArray()
     {
-      return asLongArray();
+      return isNumericNull() ? null : new Object[] {value.longValue()};
-    }
-
-    @Nullable
-    @Override
-    public Long[] asLongArray()
-    {
-      return isNumericNull() ? null : new Long[]{value.longValue()};
     }
 
     @Override
@@ -813,11 +823,11 @@ public abstract class ExprEval<T>
         case ARRAY:
           switch (castTo.getElementType().getType()) {
             case DOUBLE:
-              return ExprEval.ofDoubleArray(asDoubleArray());
+              return ExprEval.ofDoubleArray(value == null ? null : new Object[] {value.doubleValue()});
             case LONG:
-              return ExprEval.ofLongArray(asLongArray());
+              return ExprEval.ofLongArray(asArray());
             case STRING:
-              return ExprEval.ofStringArray(asStringArray());
+              return ExprEval.ofStringArray(value == null ? null : new Object[] {value.toString()});
           }
       }
       throw new IAE("invalid type " + castTo);
@@ -905,7 +915,7 @@ public abstract class ExprEval<T>
     @Override
     public Object[] asArray()
     {
-      return asStringArray();
+      return value == null ? null : new Object[] {value};
     }
 
     private int computeInt()
@@ -969,27 +979,6 @@ public abstract class ExprEval<T>
       return booleanValue;
     }
 
-    @Nullable
-    @Override
-    public String[] asStringArray()
-    {
-      return value == null ? null : new String[] {value};
-    }
-
-    @Nullable
-    @Override
-    public Long[] asLongArray()
-    {
-      return value == null ? null : new Long[] {computeLong()};
-    }
-
-    @Nullable
-    @Override
-    public Double[] asDoubleArray()
-    {
-      return value == null ? null : new Double[] {computeDouble()};
-    }
-
     @Override
     public final ExprEval castTo(ExpressionType castTo)
     {
@@ -1003,11 +992,11 @@ public abstract class ExprEval<T>
         case ARRAY:
           switch (castTo.getElementType().getType()) {
             case DOUBLE:
-              return ExprEval.ofDoubleArray(asDoubleArray());
+              return ExprEval.ofDoubleArray(value == null ? null : new Object[] {computeDouble()});
             case LONG:
-              return ExprEval.ofLongArray(asLongArray());
+              return ExprEval.ofLongArray(value == null ? null : new Object[] {computeLong()});
             case STRING:
-              return ExprEval.ofStringArray(asStringArray());
+              return ExprEval.ofStringArray(value == null ? null : new Object[] {value});
           }
       }
       throw new IAE("invalid type " + castTo);
@@ -1050,11 +1039,7 @@ public abstract class ExprEval<T>
         if (value == null) {
           cacheStringValue(null);
         } else if (value.length == 1) {
-          if (value[0] == null) {
+          cacheStringValue(Evals.asString(value[0]));
-            cacheStringValue(null);
-          } else {
-            cacheStringValue(String.valueOf(value[0]));
-          }
         } else {
           cacheStringValue(Arrays.toString(value));
         }
@@ -1166,68 +1151,6 @@ public abstract class ExprEval<T>
       return value;
     }
 
-    @Nullable
-    @Override
-    public String[] asStringArray()
-    {
-      if (value != null) {
-        if (arrayType.getElementType().is(ExprType.STRING)) {
-          return Arrays.stream(value).map(v -> (String) v).toArray(String[]::new);
-        } else if (arrayType.getElementType().isNumeric()) {
-          return Arrays.stream(value).map(x -> x != null ? x.toString() : null).toArray(String[]::new);
-        }
-      }
-      return null;
-    }
-
-    @Nullable
-    @Override
-    public Long[] asLongArray()
-    {
-      if (arrayType.getElementType().is(ExprType.LONG)) {
-        return Arrays.stream(value).map(v -> (Long) v).toArray(Long[]::new);
-      } else if (arrayType.getElementType().is(ExprType.DOUBLE)) {
-        return value == null ? null : Arrays.stream(value).map(v -> ((Double) v).longValue()).toArray(Long[]::new);
-      } else if (arrayType.getElementType().is(ExprType.STRING)) {
-        return Arrays.stream(value).map(v -> {
-          if (v == null) {
-            return null;
-          }
-          Long lv = GuavaUtils.tryParseLong((String) v);
-          if (lv == null) {
-            Double d = Doubles.tryParse((String) v);
-            if (d != null) {
-              lv = d.longValue();
-            }
-          }
-          return lv;
-        }).toArray(Long[]::new);
-      }
-      return null;
-    }
-
-    @Nullable
-    @Override
-    public Double[] asDoubleArray()
-    {
-      if (arrayType.getElementType().is(ExprType.DOUBLE)) {
-        return Arrays.stream(value).map(v -> (Double) v).toArray(Double[]::new);
-      } else if (arrayType.getElementType().is(ExprType.LONG)) {
-        return value == null ? null : Arrays.stream(value).map(v -> ((Long) v).doubleValue()).toArray(Double[]::new);
-      } else if (arrayType.getElementType().is(ExprType.STRING)) {
-        if (value == null) {
-          return null;
-        }
-        return Arrays.stream(value).map(val -> {
-          if (val == null) {
-            return null;
-          }
-          return Doubles.tryParse((String) val);
-        }).toArray(Double[]::new);
-      }
-      return new Double[0];
-    }
-
     @Override
     public ExprEval castTo(ExpressionType castTo)
     {
@@ -1346,27 +1269,6 @@ public abstract class ExprEval<T>
       return new Object[0];
     }
 
-    @Nullable
-    @Override
-    public String[] asStringArray()
-    {
-      return new String[0];
-    }
-
-    @Nullable
-    @Override
-    public Long[] asLongArray()
-    {
-      return new Long[0];
-    }
-
-    @Nullable
-    @Override
-    public Double[] asDoubleArray()
-    {
-      return new Double[0];
-    }
-
     @Override
     public ExprEval castTo(ExpressionType castTo)
     {

core/src/main/java/org/apache/druid/math/expr/Function.java

@@ -54,7 +54,6 @@ import java.util.function.BinaryOperator;
 import java.util.function.DoubleBinaryOperator;
 import java.util.function.LongBinaryOperator;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 /**
  * Base interface describing the mechanism used to evaluate a {@link FunctionExpr}. All {@link Function} implementations
@@ -507,12 +506,13 @@ public interface Function
       if (!scalarExpr.type().equals(arrayExpr.elementType())) {
         // try to cast
         ExprEval coerced = scalarExpr.castTo(arrayExpr.elementType());
-        return ExprEval.ofArray(arrayType, add(arrayType.getElementType(), arrayExpr.asArray(), coerced.value()).toArray());
+        return ExprEval.ofArray(arrayType, add(arrayType.getElementType(), arrayExpr.asArray(), coerced.value()));
-      }
-      return ExprEval.ofArray(arrayType, add(arrayType.getElementType(), arrayExpr.asArray(), scalarExpr.value()).toArray());
       }
 
-    abstract <T> Stream<T> add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val);
+      return ExprEval.ofArray(arrayType, add(arrayType.getElementType(), arrayExpr.asArray(), scalarExpr.value()));
+    }
+
+    abstract <T> Object[] add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val);
   }
 
   /**
@@ -558,13 +558,13 @@ public interface Function
       if (!lhsExpr.asArrayType().equals(rhsExpr.asArrayType())) {
         // try to cast if they types don't match
         ExprEval coerced = rhsExpr.castTo(arrayType);
-        ExprEval.ofArray(arrayType, merge(arrayType.getElementType(), lhsExpr.asArray(), coerced.asArray()).toArray());
+        ExprEval.ofArray(arrayType, merge(arrayType.getElementType(), lhsExpr.asArray(), coerced.asArray()));
       }
 
-      return ExprEval.ofArray(arrayType, merge(arrayType.getElementType(), lhsExpr.asArray(), rhsExpr.asArray()).toArray());
+      return ExprEval.ofArray(arrayType, merge(arrayType.getElementType(), lhsExpr.asArray(), rhsExpr.asArray()));
     }
 
-    abstract <T> Stream<T> merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2);
+    abstract <T> Object[] merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2);
   }
 
   abstract class ReduceFunction implements Function
@@ -3406,11 +3406,14 @@ public interface Function
     }
 
     @Override
-    <T> Stream<T> add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
+    <T> Object[] add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
     {
-      List<T> l = new ArrayList<>(Arrays.asList(array));
+      final Object[] output = new Object[array.length + 1];
-      l.add(val);
+      for (int i = 0; i < array.length; i++) {
-      return l.stream();
+        output[i] = array[i];
+      }
+      output[array.length] = val;
+      return output;
     }
   }
 
@@ -3435,11 +3438,14 @@ public interface Function
     }
 
     @Override
-    <T> Stream<T> add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
+    <T> Object[] add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
     {
-      List<T> l = new ArrayList<>(Arrays.asList(array));
+      final Object[] output = new Object[array.length + 1];
-      l.add(0, val);
+      output[0] = val;
-      return l.stream();
+      for (int i = 0; i < array.length; i++) {
+        output[i + 1] = array[i];
+      }
+      return output;
     }
   }
 
@@ -3452,11 +3458,16 @@ public interface Function
     }
 
     @Override
-    <T> Stream<T> merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2)
+    <T> Object[] merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2)
     {
-      List<T> l = new ArrayList<>(Arrays.asList(array1));
+      final Object[] output = new Object[array1.length + array2.length];
-      l.addAll(Arrays.asList(array2));
+      for (int i = 0; i < array1.length; i++) {
-      return l.stream();
+        output[i] = array1[i];
+      }
+      for (int i = array1.length, j = 0; j < array2.length; i++, j++) {
+        output[i] = array2[j];
+      }
+      return output;
     }
   }
 
@@ -3469,12 +3480,12 @@ public interface Function
     }
 
     @Override
-    <T> Stream<T> add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
+    <T> Object[] add(TypeSignature<ExprType> elementType, T[] array, @Nullable T val)
     {
-      Set<T> l = new TreeSet<>(elementType.getNullableStrategy());
+      Set<T> set = new TreeSet<>(elementType.getNullableStrategy());
-      l.addAll(Arrays.asList(array));
+      set.addAll(Arrays.asList(array));
-      l.add(val);
+      set.add(val);
-      return l.stream();
+      return set.toArray();
     }
   }
 
@@ -3487,12 +3498,12 @@ public interface Function
     }
 
     @Override
-    <T> Stream<T> merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2)
+    <T> Object[] merge(TypeSignature<ExprType> elementType, T[] array1, T[] array2)
     {
       Set<T> l = new TreeSet<>(elementType.getNullableStrategy());
       l.addAll(Arrays.asList(array1));
       l.addAll(Arrays.asList(array2));
-      return l.stream();
+      return l.toArray();
     }
   }
 
@@ -3574,7 +3585,8 @@ public interface Function
     @Override
     public ExpressionType getOutputType(Expr.InputBindingInspector inspector, List<Expr> args)
     {
-      return args.get(0).getOutputType(inspector);
+      ExpressionType arrayType = args.get(0).getOutputType(inspector);
+      return Optional.ofNullable(ExpressionType.asArrayType(arrayType)).orElse(arrayType);
     }
 
     @Override

core/src/main/java/org/apache/druid/math/expr/vector/CastToStringVectorProcessor.java

@@ -19,11 +19,10 @@
 
 package org.apache.druid.math.expr.vector;
 
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.ExpressionType;
 
-import java.util.Arrays;
-
 public final class CastToStringVectorProcessor extends CastToTypeVectorProcessor<String[]>
 {
   public CastToStringVectorProcessor(ExprVectorProcessor<?> delegate)
@@ -35,9 +34,12 @@ public final class CastToStringVectorProcessor extends CastToTypeVectorProcessor
   public ExprEvalVector<String[]> evalVector(Expr.VectorInputBinding bindings)
   {
     ExprEvalVector<?> result = delegate.evalVector(bindings);
-    return new ExprEvalStringVector(
+    final Object[] objects = result.getObjectVector();
-        Arrays.stream(result.getObjectVector()).map(x -> x != null ? x.toString() : null).toArray(String[]::new)
+    final String[] output = new String[objects.length];
-    );
+    for (int i = 0; i < objects.length; i++) {
+      output[i] = Evals.asString(objects[i]);
+    }
+    return new ExprEvalStringVector(output);
   }
 
   @Override

core/src/main/java/org/apache/druid/segment/column/ColumnType.java

@@ -26,18 +26,72 @@ import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
 
 import javax.annotation.Nullable;
 
+/**
+ * Native Druid types.
+ *
+ * @see TypeSignature
+ */
 @JsonSerialize(using = ToStringSerializer.class)
 public class ColumnType extends BaseTypeSignature<ValueType>
 {
+  /**
+   * Druid string type. Values will be represented as {@link String} or {@link java.util.List<String>} in the case
+   * of multi-value string columns. {@link ColumnType} has insufficient information to distinguish between single
+   * and multi-value strings, this requires a specific {@link TypeSignature} implementation which is supplied by
+   * segments, 'ColumnCapabilities', which is available at a higher layer and provides the method 'hasMultipleValues'.
+   *
+   * @see ValueType#STRING
+   */
   public static final ColumnType STRING = new ColumnType(ValueType.STRING, null, null);
+
+  /**
+   * Druid 64-bit integer number primitve type. Values will be represented as Java long or {@link Long}.
+   *
+   * @see ValueType#LONG
+   */
   public static final ColumnType LONG = new ColumnType(ValueType.LONG, null, null);
+  /**
+   * Druid 64-bit double precision floating point number primitive type. Values will be represented as Java double or
+   * {@link Double}.
+   *
+   * @see ValueType#DOUBLE
+   */
   public static final ColumnType DOUBLE = new ColumnType(ValueType.DOUBLE, null, null);
+  /**
+   * Druid 32-bit single precision floating point number primitive type. Values will be represented as Java float or
+   * {@link Float}.
+   *
+   * @see ValueType#FLOAT
+   */
   public static final ColumnType FLOAT = new ColumnType(ValueType.FLOAT, null, null);
   // currently, arrays only come from expressions or aggregators
   // and there are no native float expressions (or aggs which produce float arrays)
+  /**
+   * An array of Strings. Values will be represented as Object[]
+   * @see ValueType#ARRAY
+   * @see ValueType#STRING
+   */
   public static final ColumnType STRING_ARRAY = new ColumnType(ValueType.ARRAY, null, STRING);
+  /**
+   * An array of Longs. Values will be represented as Object[] or long[]
+   * @see ValueType#ARRAY
+   * @see ValueType#LONG
+   */
   public static final ColumnType LONG_ARRAY = new ColumnType(ValueType.ARRAY, null, LONG);
+  /**
+   * An array of Doubles. Values will be represented as Object[] or double[].
+   * @see ValueType#ARRAY
+   * @see ValueType#DOUBLE
+   */
   public static final ColumnType DOUBLE_ARRAY = new ColumnType(ValueType.ARRAY, null, DOUBLE);
+  /**
+   * Placeholder type for an "unknown" complex, which is used when the complex type name was "lost" or unavailable for
+   * whatever reason, to indicate an opaque type that cannot be generically handled with normal complex type handling
+   * mechanisms. Prefer to use a {@link ColumnType} with the {@link #complexTypeName} set for most complex type matters
+   * if at all possible.
+   *
+   * @see ValueType#COMPLEX
+   */
   public static final ColumnType UNKNOWN_COMPLEX = new ColumnType(ValueType.COMPLEX, null, null);
 
   @JsonCreator

core/src/main/java/org/apache/druid/segment/column/ValueType.java

@@ -63,23 +63,38 @@ public enum ValueType implements TypeDescriptor
    * String object type. This type may be used as a grouping key, an input to certain types of complex sketch
    * aggregators, and as an input to expression virtual columns. String types might potentially be 'multi-valued' when
    * stored in segments, and contextually at various layers of query processing, but this information is not available
-   * through this enum alone, and must be accompany this type indicator to properly handle.
+   * at this level.
+   *
+   * Strings are typically represented as {@link String}. Multi-value strings appear as {@link java.util.List<String>}
+   * when necessary to represent multiple values, and can vary between string and list from one row to the next.
    */
   STRING,
   /**
    * Placeholder for arbitrary 'complex' types, which have a corresponding serializer/deserializer implementation. Note
    * that knowing a type is complex alone isn't enough information to work with it directly, and additional information
-   * in the form of a type name that is registered in the complex type registry must be available to make this type
+   * in the form of a type name which must be registered in the complex type registry. Complex types are not currently
-   * meaningful. This type is not currently supported as a grouping key for aggregations, and may not be used as an
+   * supported as a grouping key for aggregations. Complex types can be used as inputs to aggregators, in cases where
-   * input to expression virtual columns, and might only be supported by the specific aggregators crafted to handle
+   * the specific aggregator supports the specific complex type. Filtering on these types with standard filters is not
-   * this complex type.
+   * well supported, and will be treated as null values.
+   *
+   * These types are represented by the individual Java type associated with the complex type name as defined in the
+   * type registry.
    */
   COMPLEX,
 
   /**
-   * Placeholder for arbitrary arrays of other {@link ValueType}. This type is not currently supported as a grouping
+   * Placeholder for arbitrary arrays of other {@link ValueType}. This type has limited support as a grouping
-   * key for aggregations, cannot be used as an input for numerical primitive aggregations such as sums, and may have
+   * key for aggregations, ARRAY of STRING, LONG, DOUBLE, and FLOAT are supported, but ARRAY types in general are not.
-   * limited support as an input among complex type sketch aggregators.
+   * ARRAY types cannot be used as an input for numerical primitive aggregations such as sums, and have limited support
+   * as an input among complex type sketch aggregators.
+   *
+   * There are currently no native ARRAY typed columns, but they may be produced by expression virtual columns,
+   * aggregators, and post-aggregators.
+   *
+   * Arrays are represented as Object[], long[], double[], or float[]. The preferred type is Object[], since the
+   * expression system is the main consumer of arrays, and the expression system uses Object[] internally. Some code
+   * represents arrays in other ways; in particular the groupBy engine and SQL result layer. Over time we expect these
+   * usages to migrate to Object[], long[], double[], and float[].
    */
   ARRAY;
 

core/src/test/java/org/apache/druid/math/expr/ExprEvalTest.java

@@ -20,6 +20,7 @@
 package org.apache.druid.math.expr;
 
 import com.google.common.collect.ImmutableList;
+import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.java.util.common.NonnullPair;
 import org.apache.druid.java.util.common.StringUtils;
@@ -131,6 +132,7 @@ public class ExprEvalTest extends InitializedNullHandlingTest
   public void testLongArraySerde()
   {
     assertExpr(0, new Long[]{1L, 2L, 3L});
+    assertExpr(0, new long[]{1L, 2L, 3L});
     assertExpr(1234, new Long[]{1L, 2L, null, 3L});
     assertExpr(1234, new Long[]{});
   }
@@ -165,6 +167,7 @@ public class ExprEvalTest extends InitializedNullHandlingTest
   public void testDoubleArraySerde()
   {
     assertExpr(0, new Double[]{1.1, 2.2, 3.3});
+    assertExpr(0, new double[]{1.1, 2.2, 3.3});
     assertExpr(1234, new Double[]{1.1, 2.2, null, 3.3});
     assertExpr(1234, new Double[]{});
   }
@@ -334,12 +337,12 @@ public class ExprEvalTest extends InitializedNullHandlingTest
   {
     ExprEval someStringArray = ExprEval.ofStringArray(new String[]{"1", "2", "foo", null, "3.3"});
     Assert.assertArrayEquals(
-        new Long[]{1L, 2L, null, null, 3L},
+        new Object[]{1L, 2L, NullHandling.defaultLongValue(), NullHandling.defaultLongValue(), 3L},
-        someStringArray.asLongArray()
+        someStringArray.castTo(ExpressionType.LONG_ARRAY).asArray()
     );
     Assert.assertArrayEquals(
-        new Double[]{1.0, 2.0, null, null, 3.3},
+        new Object[]{1.0, 2.0, NullHandling.defaultDoubleValue(), NullHandling.defaultDoubleValue(), 3.3},
-        someStringArray.asDoubleArray()
+        someStringArray.castTo(ExpressionType.DOUBLE_ARRAY).asArray()
     );
   }
 

extensions-core/multi-stage-query/src/test/java/org/apache/druid/msq/exec/MSQSelectTest.java

@@ -41,6 +41,7 @@ import org.apache.druid.query.aggregation.post.ArithmeticPostAggregator;
 import org.apache.druid.query.aggregation.post.ExpressionPostAggregator;
 import org.apache.druid.query.aggregation.post.FieldAccessPostAggregator;
 import org.apache.druid.query.dimension.DefaultDimensionSpec;
+import org.apache.druid.query.expression.TestExprMacroTable;
 import org.apache.druid.query.filter.NotDimFilter;
 import org.apache.druid.query.filter.SelectorDimFilter;
 import org.apache.druid.query.groupby.GroupByQuery;
@@ -65,6 +66,7 @@ import javax.annotation.Nonnull;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -944,6 +946,74 @@ public class MSQSelectTest extends MSQTestBase
         .verifyResults();
   }
 
+  @Test
+  public void testGroupByArrayWithMultiValueMvToArray()
+  {
+    Map<String, Object> context = ImmutableMap.<String, Object>builder()
+                                              .putAll(DEFAULT_MSQ_CONTEXT)
+                                              .put("groupByEnableMultiValueUnnesting", true)
+                                              .build();
+
+    RowSignature rowSignature = RowSignature.builder()
+                                            .add("EXPR$0", ColumnType.STRING_ARRAY)
+                                            .add("cnt1", ColumnType.LONG)
+                                            .build();
+
+    ArrayList<Object[]> expected = new ArrayList<>();
+    expected.add(new Object[]{Collections.singletonList(null), !useDefault ? 2L : 3L});
+    if (!useDefault) {
+      expected.add(new Object[]{Collections.singletonList(""), 1L});
+    }
+    expected.addAll(ImmutableList.of(
+        new Object[]{Arrays.asList("a", "b"), 1L},
+        new Object[]{Arrays.asList("b", "c"), 1L},
+        new Object[]{Collections.singletonList("d"), 1L}
+    ));
+
+    testSelectQuery()
+        .setSql("select MV_TO_ARRAY(dim3), count(*) as cnt1 from foo group by MV_TO_ARRAY(dim3)")
+        .setQueryContext(context)
+        .setExpectedMSQSpec(MSQSpec.builder()
+                                   .query(GroupByQuery.builder()
+                                                      .setDataSource(CalciteTests.DATASOURCE1)
+                                                      .setInterval(querySegmentSpec(Filtration.eternity()))
+                                                      .setGranularity(Granularities.ALL)
+                                                      .setDimensions(
+                                                          dimensions(
+                                                              new DefaultDimensionSpec(
+                                                                  "v0",
+                                                                  "d0",
+                                                                  ColumnType.STRING_ARRAY
+                                                              )
+                                                          )
+                                                      )
+                                                      .setVirtualColumns(
+                                                          new ExpressionVirtualColumn(
+                                                              "v0",
+                                                              "mv_to_array(\"dim3\")",
+                                                              ColumnType.STRING_ARRAY,
+                                                              TestExprMacroTable.INSTANCE
+                                                          )
+                                                      )
+                                                      .setAggregatorSpecs(aggregators(new CountAggregatorFactory("a0")))
+                                                      .setContext(context)
+                                                      .build()
+                                   )
+                                   .columnMappings(
+                                       new ColumnMappings(
+                                           ImmutableList.of(
+                                               new ColumnMapping("d0", "EXPR$0"),
+                                               new ColumnMapping("a0", "cnt1")
+                                           )
+                                       )
+                                   )
+                                   .tuningConfig(MSQTuningConfig.defaultConfig())
+                                   .build())
+        .setExpectedRowSignature(rowSignature)
+        .setExpectedResultRows(expected)
+        .verifyResults();
+  }
+
   @Test
   public void testGroupByWithMultiValueMvToArrayWithoutGroupByEnable()
   {

processing/src/main/java/org/apache/druid/frame/write/FrameWriterUtils.java

@@ -147,9 +147,9 @@ public class FrameWriterUtils
       for (int i = 0; i < ((List<?>) row).size(); i++) {
         retVal.add(getUtf8ByteBufferFromString(((List<String>) row).get(i)));
       }
-    } else if (row instanceof String[]) {
+    } else if (row instanceof Object[]) {
-      for (String value : (String[]) row) {
+      for (Object value : (Object[]) row) {
-        retVal.add(getUtf8ByteBufferFromString(value));
+        retVal.add(getUtf8ByteBufferFromString((String) value));
       }
     } else if (row instanceof ComparableStringArray) {
       for (String value : ((ComparableStringArray) row).getDelegate()) {

processing/src/main/java/org/apache/druid/segment/filter/ExpressionFilter.java

@@ -141,26 +141,26 @@ public class ExpressionFilter implements Filter
         if (eval.type().isArray()) {
           switch (eval.elementType().getType()) {
             case LONG:
-              final Long[] lResult = eval.asLongArray();
+              final Object[] lResult = eval.asArray();
               if (lResult == null) {
                 return false;
               }
 
-              return Arrays.stream(lResult).filter(Objects::nonNull).anyMatch(Evals::asBoolean);
+              return Arrays.stream(lResult).filter(Objects::nonNull).anyMatch(o -> Evals.asBoolean((long) o));
             case STRING:
-              final String[] sResult = eval.asStringArray();
+              final Object[] sResult = eval.asArray();
               if (sResult == null) {
                 return false;
               }
 
-              return Arrays.stream(sResult).anyMatch(Evals::asBoolean);
+              return Arrays.stream(sResult).anyMatch(o -> Evals.asBoolean((String) o));
             case DOUBLE:
-              final Double[] dResult = eval.asDoubleArray();
+              final Object[] dResult = eval.asArray();
               if (dResult == null) {
                 return false;
               }
 
-              return Arrays.stream(dResult).filter(Objects::nonNull).anyMatch(Evals::asBoolean);
+              return Arrays.stream(dResult).filter(Objects::nonNull).anyMatch(o -> Evals.asBoolean((double) o));
           }
         }
         return eval.asBoolean();

processing/src/main/java/org/apache/druid/segment/transform/ExpressionTransform.java

@@ -99,7 +99,13 @@ public class ExpressionTransform implements Transform
     @Override
     public Object eval(final Row row)
     {
-      return ExpressionSelectors.coerceEvalToSelectorObject(
+      // this will need adjusted if we want to allow expression transforms to produce true arrays. Currently, calling
+      // this method will coerce any expression output into:
+      //    - the expression value if the value is not an array
+      //    - the single array element if the value is an array with 1 element
+      //    - a list with all of the array elements if the value is an array with more than 1 element
+      // and so is tuned towards multi-value strings
+      return ExpressionSelectors.coerceEvalToObjectOrList(
           expr.eval(InputBindings.forFunction(name -> getValueFromRow(row, name)))
       );
     }

processing/src/main/java/org/apache/druid/segment/virtual/ExpressionMultiValueDimensionSelector.java

@@ -21,6 +21,7 @@ package org.apache.druid.segment.virtual;
 
 import com.google.common.base.Predicate;
 import org.apache.druid.common.config.NullHandling;
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.ExprEval;
 import org.apache.druid.query.extraction.ExtractionFn;
 import org.apache.druid.query.filter.ValueMatcher;
@@ -71,26 +72,22 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
   String getValue(ExprEval evaluated)
   {
     assert !evaluated.isArray();
-    return NullHandling.emptyToNullIfNeeded(evaluated.asString());
+    return evaluated.asString();
   }
 
-  List<String> getArray(ExprEval evaluated)
+  List<String> getArrayAsList(ExprEval evaluated)
   {
     assert evaluated.isArray();
     //noinspection ConstantConditions
-    return Arrays.stream(evaluated.asStringArray())
+    return Arrays.stream(evaluated.asArray())
-                 .map(NullHandling::emptyToNullIfNeeded)
+                 .map(Evals::asString)
                  .collect(Collectors.toList());
   }
 
   @Nullable
   String getArrayValue(ExprEval evaluated, int i)
   {
-    assert evaluated.isArray();
+    return getArrayElement(evaluated, i);
-    String[] stringArray = evaluated.asStringArray();
-    //noinspection ConstantConditions because of assert statement above
-    assert i < stringArray.length;
-    return NullHandling.emptyToNullIfNeeded(stringArray[i]);
   }
 
   @Override
@@ -121,7 +118,7 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
       return getArrayValue(evaluated, id);
     }
     assert id == 0;
-    return NullHandling.emptyToNullIfNeeded(evaluated.asString());
+    return evaluated.asString();
   }
 
   @Override
@@ -134,7 +131,7 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
       {
         ExprEval evaluated = getEvaluated();
         if (evaluated.isArray()) {
-          List<String> array = getArray(evaluated);
+          List<String> array = getArrayAsList(evaluated);
           return array.stream().anyMatch(x -> Objects.equals(x, value));
         }
         return Objects.equals(getValue(evaluated), value);
@@ -158,7 +155,7 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
       {
         ExprEval evaluated = getEvaluated();
         if (evaluated.isArray()) {
-          List<String> array = getArray(evaluated);
+          List<String> array = getArrayAsList(evaluated);
           return array.stream().anyMatch(x -> predicate.apply(x));
         }
         return predicate.apply(getValue(evaluated));
@@ -198,7 +195,7 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
   {
     ExprEval evaluated = getEvaluated();
     if (evaluated.isArray()) {
-      return getArray(evaluated);
+      return getArrayAsList(evaluated);
     }
     return getValue(evaluated);
   }
@@ -230,21 +227,18 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
     }
 
     @Override
-    List<String> getArray(ExprEval evaluated)
+    List<String> getArrayAsList(ExprEval evaluated)
     {
       assert evaluated.isArray();
-      return Arrays.stream(evaluated.asStringArray())
+      return Arrays.stream(evaluated.asArray())
-                   .map(x -> extractionFn.apply(NullHandling.emptyToNullIfNeeded(x)))
+                   .map(x -> extractionFn.apply(Evals.asString(x)))
                    .collect(Collectors.toList());
     }
 
     @Override
     String getArrayValue(ExprEval evaluated, int i)
     {
-      assert evaluated.isArray();
+      return extractionFn.apply(ExpressionMultiValueDimensionSelector.getArrayElement(evaluated, i));
-      String[] stringArray = evaluated.asStringArray();
-      assert i < stringArray.length;
-      return extractionFn.apply(NullHandling.emptyToNullIfNeeded(stringArray[i]));
     }
 
     @Override
@@ -254,4 +248,14 @@ public class ExpressionMultiValueDimensionSelector implements DimensionSelector
       inspector.visit("extractionFn", extractionFn);
     }
   }
+
+  @Nullable
+  private static String getArrayElement(ExprEval eval, int i)
+  {
+    final Object[] stringArray = eval.asArray();
+    if (stringArray == null) {
+      return null;
+    }
+    return Evals.asString(stringArray[i]);
+  }
 }

processing/src/main/java/org/apache/druid/segment/virtual/ExpressionSelectors.java

@@ -26,6 +26,7 @@ import com.google.common.collect.Iterables;
 import org.apache.druid.common.config.NullHandling;
 import org.apache.druid.java.util.common.NonnullPair;
 import org.apache.druid.java.util.common.Pair;
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.ExprEval;
 import org.apache.druid.math.expr.ExpressionProcessing;
@@ -109,7 +110,66 @@ public class ExpressionSelectors
       {
         // No need for null check on getObject() since baseSelector impls will never return null.
         ExprEval eval = baseSelector.getObject();
-        return coerceEvalToSelectorObject(eval);
+        return eval.value();
+      }
+
+      @Override
+      public Class classOfObject()
+      {
+        return Object.class;
+      }
+
+      @Override
+      public void inspectRuntimeShape(RuntimeShapeInspector inspector)
+      {
+        inspector.visit("baseSelector", baseSelector);
+      }
+    };
+  }
+
+  public static ColumnValueSelector makeStringColumnValueSelector(
+      ColumnSelectorFactory columnSelectorFactory,
+      Expr expression
+  )
+  {
+    final ColumnValueSelector<ExprEval> baseSelector = makeExprEvalSelector(columnSelectorFactory, expression);
+
+    return new ColumnValueSelector()
+    {
+      @Override
+      public double getDouble()
+      {
+        // No Assert for null handling as baseSelector already have it.
+        return baseSelector.getDouble();
+      }
+
+      @Override
+      public float getFloat()
+      {
+        // No Assert for null handling as baseSelector already have it.
+        return baseSelector.getFloat();
+      }
+
+      @Override
+      public long getLong()
+      {
+        // No Assert for null handling as baseSelector already have it.
+        return baseSelector.getLong();
+      }
+
+      @Override
+      public boolean isNull()
+      {
+        return baseSelector.isNull();
+      }
+
+      @Nullable
+      @Override
+      public Object getObject()
+      {
+        // No need for null check on getObject() since baseSelector impls will never return null.
+        ExprEval eval = baseSelector.getObject();
+        return coerceEvalToObjectOrList(eval);
       }
 
       @Override
@@ -208,8 +268,14 @@ public class ExpressionSelectors
     if (baseSelector instanceof ConstantExprEvalSelector) {
       // Optimization for dimension selectors on constants.
       if (plan.is(ExpressionPlan.Trait.NON_SCALAR_OUTPUT)) {
-        final String[] value = baseSelector.getObject().asStringArray();
+        final Object[] value = baseSelector.getObject().asArray();
-        return DimensionSelector.multiConstant(value == null ? null : Arrays.asList(value), extractionFn);
+        final List<String> stringList;
+        if (value != null) {
+          stringList = Arrays.stream(value).map(Evals::asString).collect(Collectors.toList());
+        } else {
+          stringList = null;
+        }
+        return DimensionSelector.multiConstant(stringList, extractionFn);
       }
       return DimensionSelector.constant(baseSelector.getObject().asString(), extractionFn);
     } else if (baseSelector instanceof NilColumnValueSelector) {
@@ -460,17 +526,27 @@ public class ExpressionSelectors
   }
 
   /**
-   * Coerces {@link ExprEval} value back to selector friendly {@link List} if the evaluated expression result is an
+   * Coerces {@link ExprEval} value back to a {@link ColumnType#STRING} selector friendly value, converting into:
-   * array type
+   *    - the expression value if the value is not an array
+   *    - the single array element if the value is an array with 1 element
+   *    - a list with all of the array elements if the value is an array with more than 1 element
+   * This method is used by {@link #makeStringColumnValueSelector(ColumnSelectorFactory, Expr)}, which is used
+   * exclusively for making {@link ColumnValueSelector} when an {@link ExpressionVirtualColumn} has STRING output type,
+   * and by {@link org.apache.druid.segment.transform.ExpressionTransform} which should be reconsidered if we ever
+   * want to add support for ingestion transforms producing {@link ValueType#ARRAY} typed outputs.
    */
   @Nullable
-  public static Object coerceEvalToSelectorObject(ExprEval eval)
+  public static Object coerceEvalToObjectOrList(ExprEval eval)
   {
     if (eval.type().isArray()) {
       final Object[] asArray = eval.asArray();
-      return asArray == null
+      if (asArray == null) {
-             ? null
+        return null;
-             : Arrays.stream(asArray).collect(Collectors.toList());
+      }
+      if (asArray.length == 1) {
+        return asArray[0];
+      }
+      return Arrays.stream(asArray).collect(Collectors.toList());
     }
     return eval.value();
   }

processing/src/main/java/org/apache/druid/segment/virtual/ExpressionVirtualColumn.java

@@ -42,6 +42,7 @@ import org.apache.druid.segment.VirtualColumn;
 import org.apache.druid.segment.column.ColumnCapabilities;
 import org.apache.druid.segment.column.ColumnCapabilitiesImpl;
 import org.apache.druid.segment.column.ColumnType;
+import org.apache.druid.segment.column.ValueType;
 import org.apache.druid.segment.vector.SingleValueDimensionVectorSelector;
 import org.apache.druid.segment.vector.VectorColumnSelectorFactory;
 import org.apache.druid.segment.vector.VectorObjectSelector;
@@ -140,6 +141,13 @@ public class ExpressionVirtualColumn implements VirtualColumn
   @Override
   public ColumnValueSelector<?> makeColumnValueSelector(String columnName, ColumnSelectorFactory factory)
   {
+    final ColumnCapabilities capabilities = capabilities(factory, name);
+    // we make a special column value selector for values that are expected to be STRING to conform to behavior of
+    // other single and multi-value STRING selectors, whose getObject is expected to produce a single STRING value
+    // or List of STRING values.
+    if (capabilities.is(ValueType.STRING)) {
+      return ExpressionSelectors.makeStringColumnValueSelector(factory, parsedExpression.get());
+    }
     return ExpressionSelectors.makeColumnValueSelector(factory, parsedExpression.get());
   }
 

processing/src/test/java/org/apache/druid/segment/virtual/ExpressionSelectorsTest.java

@@ -599,17 +599,17 @@ public class ExpressionSelectorsTest extends InitializedNullHandlingTest
   {
     Assert.assertEquals(
         ImmutableList.of(1L, 2L, 3L),
-        ExpressionSelectors.coerceEvalToSelectorObject(ExprEval.ofLongArray(new Long[]{1L, 2L, 3L}))
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofLongArray(new Long[]{1L, 2L, 3L}))
     );
 
     Assert.assertEquals(
         ImmutableList.of(1.0, 2.0, 3.0),
-        ExpressionSelectors.coerceEvalToSelectorObject(ExprEval.ofDoubleArray(new Double[]{1.0, 2.0, 3.0}))
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofDoubleArray(new Double[]{1.0, 2.0, 3.0}))
     );
 
     Assert.assertEquals(
         ImmutableList.of("a", "b", "c"),
-        ExpressionSelectors.coerceEvalToSelectorObject(ExprEval.ofStringArray(new String[]{"a", "b", "c"}))
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofStringArray(new String[]{"a", "b", "c"}))
     );
 
     List<String> withNulls = new ArrayList<>();
@@ -618,7 +618,18 @@ public class ExpressionSelectorsTest extends InitializedNullHandlingTest
     withNulls.add("c");
     Assert.assertEquals(
         withNulls,
-        ExpressionSelectors.coerceEvalToSelectorObject(ExprEval.ofStringArray(new String[]{"a", null, "c"}))
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofStringArray(new String[]{"a", null, "c"}))
+    );
+
+    Assert.assertNull(
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofLongArray(null))
+    );
+    Assert.assertEquals(
+        1L,
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofLongArray(new Long[]{1L}))
+    );
+    Assert.assertNull(
+        ExpressionSelectors.coerceEvalToObjectOrList(ExprEval.ofLongArray(new Long[]{null}))
     );
   }
 

sql/src/main/java/org/apache/druid/sql/calcite/expression/builtin/ArrayContainsOperatorConversion.java

@@ -25,6 +25,7 @@ import org.apache.calcite.sql.SqlFunction;
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.ExprEval;
 import org.apache.druid.math.expr.InputBindings;
@@ -104,7 +105,7 @@ public class ArrayContainsOperatorConversion extends BaseExpressionDimFilterOper
         // Evaluate the expression to get out the array elements.
         // We can safely pass a noop ObjectBinding if the expression is literal.
         ExprEval<?> exprEval = expr.eval(InputBindings.nilBindings());
-        String[] arrayElements = exprEval.asStringArray();
+        Object[] arrayElements = exprEval.asArray();
         if (arrayElements == null || arrayElements.length == 0) {
           // If arrayElements is empty which means rightExpr is an empty array,
           // it is technically more correct to return a TrueDimFiler here.
@@ -112,11 +113,11 @@ public class ArrayContainsOperatorConversion extends BaseExpressionDimFilterOper
           // to create an empty array with no argument, we just return null.
           return null;
         } else if (arrayElements.length == 1) {
-          return newSelectorDimFilter(leftExpr.getSimpleExtraction(), arrayElements[0]);
+          return newSelectorDimFilter(leftExpr.getSimpleExtraction(), Evals.asString(arrayElements[0]));
         } else {
           final List<DimFilter> selectFilters = Arrays
               .stream(arrayElements)
-              .map(val -> newSelectorDimFilter(leftExpr.getSimpleExtraction(), val))
+              .map(val -> newSelectorDimFilter(leftExpr.getSimpleExtraction(), Evals.asString(val)))
               .collect(Collectors.toList());
           return new AndDimFilter(selectFilters);
         }

sql/src/main/java/org/apache/druid/sql/calcite/expression/builtin/ArrayOverlapOperatorConversion.java

@@ -25,6 +25,7 @@ import org.apache.calcite.sql.SqlFunction;
 import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.ExprEval;
 import org.apache.druid.math.expr.InputBindings;
@@ -41,6 +42,7 @@ import org.apache.druid.sql.calcite.rel.VirtualColumnRegistry;
 import javax.annotation.Nullable;
 import java.util.Arrays;
 import java.util.List;
+import java.util.stream.Collectors;
 
 public class ArrayOverlapOperatorConversion extends BaseExpressionDimFilterOperatorConversion
 {
@@ -111,7 +113,7 @@ public class ArrayOverlapOperatorConversion extends BaseExpressionDimFilterOpera
       // Evaluate the expression to take out the array elements.
       // We can safely pass null if the expression is literal.
       ExprEval<?> exprEval = expr.eval(InputBindings.nilBindings());
-      String[] arrayElements = exprEval.asStringArray();
+      Object[] arrayElements = exprEval.asArray();
       if (arrayElements == null || arrayElements.length == 0) {
         // If arrayElements is empty which means complexExpr is an empty array,
         // it is technically more correct to return a TrueDimFiler here.
@@ -119,11 +121,11 @@ public class ArrayOverlapOperatorConversion extends BaseExpressionDimFilterOpera
         // to create an empty array with no argument, we just return null.
         return null;
       } else if (arrayElements.length == 1) {
-        return newSelectorDimFilter(simpleExtractionExpr.getSimpleExtraction(), arrayElements[0]);
+        return newSelectorDimFilter(simpleExtractionExpr.getSimpleExtraction(), Evals.asString(arrayElements[0]));
       } else {
         return new InDimFilter(
             simpleExtractionExpr.getSimpleExtraction().getColumn(),
-            new InDimFilter.ValuesSet(Arrays.asList(arrayElements)),
+            new InDimFilter.ValuesSet(Arrays.stream(arrayElements).map(Evals::asString).collect(Collectors.toList())),
             simpleExtractionExpr.getSimpleExtraction().getExtractionFn(),
             null
         );

sql/src/main/java/org/apache/druid/sql/calcite/expression/builtin/MultiValueStringOperatorConversions.java

@@ -29,6 +29,7 @@ import org.apache.calcite.sql.type.OperandTypes;
 import org.apache.calcite.sql.type.ReturnTypes;
 import org.apache.calcite.sql.type.SqlTypeFamily;
 import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.druid.math.expr.Evals;
 import org.apache.druid.math.expr.Expr;
 import org.apache.druid.math.expr.InputBindings;
 import org.apache.druid.math.expr.Parser;
@@ -44,7 +45,6 @@ import org.apache.druid.sql.calcite.planner.Calcites;
 import org.apache.druid.sql.calcite.planner.PlannerContext;
 
 import javax.annotation.Nullable;
-import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 
@@ -338,12 +338,14 @@ public class MultiValueStringOperatorConversions
       if (!expr.isLiteral()) {
         return null;
       }
-      String[] lit = expr.eval(InputBindings.nilBindings()).asStringArray();
+      Object[] lit = expr.eval(InputBindings.nilBindings()).asArray();
       if (lit == null || lit.length == 0) {
         return null;
       }
       HashSet<String> literals = Sets.newHashSetWithExpectedSize(lit.length);
-      literals.addAll(Arrays.asList(lit));
+      for (Object o : lit) {
+        literals.add(Evals.asString(o));
+      }
 
       final DruidExpression.ExpressionGenerator builder = (args) -> {
         final StringBuilder expressionBuilder;

sql/src/main/java/org/apache/druid/sql/calcite/planner/DruidRexExecutor.java

@@ -144,22 +144,32 @@ public class DruidRexExecutor implements RexExecutor
           assert exprResult.isArray();
           if (SqlTypeName.NUMERIC_TYPES.contains(constExp.getType().getComponentType().getSqlTypeName())) {
             if (exprResult.type().getElementType().is(ExprType.LONG)) {
-              List<BigDecimal> resultAsBigDecimalList = Arrays.stream(exprResult.asLongArray())
+              List<BigDecimal> resultAsBigDecimalList = Arrays.stream(exprResult.asArray())
-                                                              .map(BigDecimal::valueOf)
+                                                              .map(val -> {
+                                                                final Number longVal = (Number) val;
+                                                                if (longVal == null) {
+                                                                  return null;
+                                                                }
+                                                                return BigDecimal.valueOf(longVal.longValue());
+                                                              })
                                                               .collect(Collectors.toList());
               literal = rexBuilder.makeLiteral(resultAsBigDecimalList, constExp.getType(), true);
             } else {
-              List<BigDecimal> resultAsBigDecimalList = Arrays.stream(exprResult.asDoubleArray()).map(
+              List<BigDecimal> resultAsBigDecimalList = Arrays.stream(exprResult.asArray()).map(
-                  doubleVal -> {
+                  val -> {
-                    if (Double.isNaN(doubleVal) || Double.isInfinite(doubleVal)) {
+                    final Number doubleVal = (Number) val;
+                    if (doubleVal == null) {
+                      return null;
+                    }
+                    if (Double.isNaN(doubleVal.doubleValue()) || Double.isInfinite(doubleVal.doubleValue())) {
                       String expression = druidExpression.getExpression();
                       throw new UnsupportedSQLQueryException(
                           "'%s' contains an element that evaluates to '%s' which is not supported in SQL. You can either cast the element in the array to bigint or char or change the expression itself",
                           expression,
-                          Double.toString(doubleVal)
+                          Double.toString(doubleVal.doubleValue())
                       );
                     }
-                    return BigDecimal.valueOf(doubleVal);
+                    return BigDecimal.valueOf(doubleVal.doubleValue());
                   }
               ).collect(Collectors.toList());
               literal = rexBuilder.makeLiteral(resultAsBigDecimalList, constExp.getType(), true);

sql/src/main/java/org/apache/druid/sql/calcite/run/NativeQueryMaker.java

@@ -21,6 +21,7 @@ package org.apache.druid.sql.calcite.run;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.Iterables;
 import com.google.common.primitives.Ints;
 import it.unimi.dsi.fastutil.objects.Object2IntMap;
@@ -355,7 +356,8 @@ public class NativeQueryMaker implements QueryMaker
   }
 
 
-  private static Object maybeCoerceArrayToList(Object value, boolean mustCoerce)
+  @VisibleForTesting
+  static Object maybeCoerceArrayToList(Object value, boolean mustCoerce)
   {
     if (value instanceof List) {
       return value;
@@ -366,12 +368,23 @@ public class NativeQueryMaker implements QueryMaker
     } else if (value instanceof Double[]) {
       return Arrays.asList((Double[]) value);
     } else if (value instanceof Object[]) {
-      Object[] array = (Object[]) value;
+      final Object[] array = (Object[]) value;
-      ArrayList<Object> lst = new ArrayList<>(array.length);
+      final ArrayList<Object> lst = new ArrayList<>(array.length);
       for (Object o : array) {
         lst.add(maybeCoerceArrayToList(o, false));
       }
       return lst;
+    } else if (value instanceof long[]) {
+      return Arrays.stream((long[]) value).boxed().collect(Collectors.toList());
+    } else if (value instanceof double[]) {
+      return Arrays.stream((double[]) value).boxed().collect(Collectors.toList());
+    } else if (value instanceof float[]) {
+      final float[] array = (float[]) value;
+      final ArrayList<Object> lst = new ArrayList<>(array.length);
+      for (float f : array) {
+        lst.add(f);
+      }
+      return lst;
     } else if (value instanceof ComparableStringArray) {
       return Arrays.asList(((ComparableStringArray) value).getDelegate());
     } else if (value instanceof ComparableList) {

sql/src/test/java/org/apache/druid/sql/calcite/CalciteMultiValueStringQueryTest.java

@@ -178,7 +178,7 @@ public class CalciteMultiValueStringQueryTest extends BaseCalciteQueryTest
   @Test
   public void testMultiValueStringWorksLikeStringScan()
   {
-    final String nullVal = NullHandling.replaceWithDefault() ? "[\"foo\"]" : "[null]";
+    final String nullVal = NullHandling.replaceWithDefault() ? "foo" : null;
     testQuery(
         "SELECT concat(dim3, 'foo') FROM druid.numfoo",
         ImmutableList.of(
@@ -195,8 +195,8 @@ public class CalciteMultiValueStringQueryTest extends BaseCalciteQueryTest
         ImmutableList.of(
             new Object[]{"[\"afoo\",\"bfoo\"]"},
             new Object[]{"[\"bfoo\",\"cfoo\"]"},
-            new Object[]{"[\"dfoo\"]"},
+            new Object[]{"dfoo"},
-            new Object[]{"[\"foo\"]"},
+            new Object[]{"foo"},
             new Object[]{nullVal},
             new Object[]{nullVal}
         )
@@ -206,7 +206,7 @@ public class CalciteMultiValueStringQueryTest extends BaseCalciteQueryTest
   @Test
   public void testMultiValueStringWorksLikeStringSelfConcatScan()
   {
-    final String nullVal = NullHandling.replaceWithDefault() ? "[\"-lol-\"]" : "[null]";
+    final String nullVal = NullHandling.replaceWithDefault() ? "-lol-" : null;
     testQuery(
         "SELECT concat(dim3, '-lol-', dim3) FROM druid.numfoo",
         ImmutableList.of(
@@ -223,8 +223,8 @@ public class CalciteMultiValueStringQueryTest extends BaseCalciteQueryTest
         ImmutableList.of(
             new Object[]{"[\"a-lol-a\",\"b-lol-b\"]"},
             new Object[]{"[\"b-lol-b\",\"c-lol-c\"]"},
-            new Object[]{"[\"d-lol-d\"]"},
+            new Object[]{"d-lol-d"},
-            new Object[]{"[\"-lol-\"]"},
+            new Object[]{"-lol-"},
             new Object[]{nullVal},
             new Object[]{nullVal}
         )
@@ -387,8 +387,8 @@ public class CalciteMultiValueStringQueryTest extends BaseCalciteQueryTest
                 .build()
         ),
         ImmutableList.of(
-            new Object[]{"[\"b\"]"},
+            new Object[]{"b"},
-            new Object[]{"[\"c\"]"},
+            new Object[]{"c"},
             new Object[]{"[]"},
             new Object[]{useDefault ? NULL_STRING : "[]"},
             new Object[]{NULL_STRING},

sql/src/test/java/org/apache/druid/sql/calcite/run/NativeQueryMakerTest.java

@@ -0,0 +1,116 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.sql.calcite.run;
+
+import org.apache.druid.segment.data.ComparableList;
+import org.apache.druid.segment.data.ComparableStringArray;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class NativeQueryMakerTest
+{
+
+  @Test
+  public void testCoerceStringArrays()
+  {
+    final List<String> stringList = Arrays.asList("x", "y", "z", null);
+    final Object[] stringArray = new Object[]{"x", "y", "z", null};
+    final ComparableStringArray comparableStringArray = ComparableStringArray.of(new String[]{"x", "y", "z", null});
+    final String[] stringArray2 = new String[]{"x", "y", "z", null};
+
+    assertCoerced(stringList, stringList, true);
+    assertCoerced(stringList, stringArray, true);
+    assertCoerced(stringList, stringArray2, true);
+    assertCoerced(stringList, comparableStringArray, true);
+  }
+
+  @Test
+  public void testCoerceLongArrays()
+  {
+    final List<Long> listWithNull = Arrays.asList(1L, 2L, null, 3L);
+    final Long[] arrayWithNull = new Long[]{1L, 2L, null, 3L};
+    final ComparableList<Long> comparableList = new ComparableList<>(listWithNull);
+    final List<Long> list = Arrays.asList(1L, 2L, 3L);
+    final long[] array = new long[]{1L, 2L, 3L};
+
+    assertCoerced(listWithNull, listWithNull, true);
+    assertCoerced(listWithNull, arrayWithNull, true);
+    assertCoerced(listWithNull, comparableList, true);
+    assertCoerced(list, list, true);
+    assertCoerced(list, array, true);
+  }
+
+  @Test
+  public void testCoerceDoubleArrays()
+  {
+    final List<Double> listWithNull = Arrays.asList(1.1, 2.2, null, 3.3);
+    final Double[] arrayWithNull = new Double[]{1.1, 2.2, null, 3.3};
+    final ComparableList<Double> comparableList = new ComparableList<>(listWithNull);
+    final List<Double> list = Arrays.asList(1.1, 2.2, 3.3);
+    final double[] array = new double[]{1.1, 2.2, 3.3};
+
+    assertCoerced(listWithNull, listWithNull, true);
+    assertCoerced(listWithNull, arrayWithNull, true);
+    assertCoerced(listWithNull, comparableList, true);
+    assertCoerced(list, list, true);
+    assertCoerced(list, array, true);
+  }
+
+  @Test
+  public void testCoerceFloatArrays()
+  {
+    final List<Float> listWithNull = Arrays.asList(1.1f, 2.2f, null, 3.3f);
+    final Float[] arrayWithNull = new Float[]{1.1f, 2.2f, null, 3.3f};
+    final ComparableList<Float> comparableList = new ComparableList<>(listWithNull);
+    final List<Float> list = Arrays.asList(1.1f, 2.2f, 3.3f);
+    final float[] array = new float[]{1.1f, 2.2f, 3.3f};
+
+    assertCoerced(listWithNull, listWithNull, true);
+    assertCoerced(listWithNull, arrayWithNull, true);
+    assertCoerced(listWithNull, comparableList, true);
+    assertCoerced(list, list, true);
+    assertCoerced(list, array, true);
+  }
+
+  @Test
+  public void testCoerceNestedArrays()
+  {
+    List<?> nestedList = Arrays.asList(Arrays.asList(1L, 2L, 3L), Arrays.asList(4L, 5L, 6L));
+    Object[] nestedArray = new Object[]{new Object[]{1L, 2L, 3L}, new Object[]{4L, 5L, 6L}};
+
+    assertCoerced(nestedList, nestedList, true);
+    assertCoerced(nestedList, nestedArray, true);
+  }
+
+  @Test
+  public void testMustCoerce()
+  {
+    Assert.assertNull(NativeQueryMaker.maybeCoerceArrayToList("hello", true));
+  }
+
+  private static void assertCoerced(Object expected, Object toCoerce, boolean mustCoerce)
+  {
+    Object coerced = NativeQueryMaker.maybeCoerceArrayToList(toCoerce, mustCoerce);
+    Assert.assertEquals(expected, coerced);
+  }
+}