Support LPAD and RPAD sql function (#7388)

* lpad and rpad sql function

* feedback address

* feedback address

* add doc and format

* update docs

core/src/main/java/org/apache/druid/java/util/common/StringUtils.java

@@ -411,4 +411,80 @@ public class StringUtils
     System.arraycopy(multiple, 0, multiple, copied, limit - copied);
     return new String(multiple, StandardCharsets.UTF_8);
   }
+   
+  /**
+   * Returns the string left-padded with the string pad to a length of len characters.
+   * If str is longer than len, the return value is shortened to len characters.
+   * Lpad and rpad functions are migrated from flink's scala function with minor refactor
+   * https://github.com/apache/flink/blob/master/flink-table/flink-table-planner/src/main/scala/org/apache/flink/table/runtime/functions/ScalarFunctions.scala
+   *
+   * @param base The base string to be padded
+   * @param len The length of padded string
+   * @param pad The pad string
+   * @return the string left-padded with pad to a length of len
+   */
+  public static String lpad(String base, Integer len, String pad)
+  {
+    if (len < 0) {
+      return null;
+    } else if (len == 0) {
+      return "";
+    }
+
+    char[] data = new char[len];
+
+    // The length of the padding needed
+    int pos = Math.max(len - base.length(), 0);
+
+    // Copy the padding
+    for (int i = 0; i < pos; i += pad.length()) {
+      for (int j = 0; j < pad.length() && j < pos - i; j++) {
+        data[i + j] = pad.charAt(j);
+      }
+    }
+
+    // Copy the base
+    for (int i = 0; pos + i < len && i < base.length(); i++) {
+      data[pos + i] = base.charAt(i);
+    }
+
+    return new String(data);
+  }
+
+  /**
+   * Returns the string right-padded with the string pad to a length of len characters.
+   * If str is longer than len, the return value is shortened to len characters. 
+   *
+   * @param base The base string to be padded
+   * @param len The length of padded string
+   * @param pad The pad string
+   * @return the string right-padded with pad to a length of len
+   */
+  public static String rpad(String base, Integer len, String pad)
+  {
+    if (len < 0) {
+      return null;
+    } else if (len == 0) {
+      return "";
+    }
+
+    char[] data = new char[len];
+
+    int pos = 0;
+
+    // Copy the base
+    for ( ; pos < base.length() && pos < len; pos++) {
+      data[pos] = base.charAt(pos);
+    }
+
+    // Copy the padding
+    for ( ; pos < len; pos += pad.length()) {
+      for (int i = 0; i < pad.length() && i < len - pos; i++) {
+        data[pos + i] = pad.charAt(i);
+      }
+    }
+
+    return new String(data);
+  }
+
 }

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

@@ -1367,4 +1367,61 @@ interface Function
       return ExprEval.of(expr.value() != null, ExprType.LONG);
     }
   }
+
+  class LpadFunc implements Function
+  {
+    @Override
+    public String name()
+    {
+      return "lpad";
+    }
+
+    @Override
+    public ExprEval apply(List<Expr> args, Expr.ObjectBinding bindings)
+    {
+      if (args.size() != 3) {
+        throw new IAE("Function[%s] needs 3 arguments", name());
+      }
+      
+      String base = args.get(0).eval(bindings).asString();
+      int len = args.get(1).eval(bindings).asInt();
+      String pad = args.get(2).eval(bindings).asString();
+
+      if (base == null || pad == null) {
+        return ExprEval.of(null);
+      } else {
+        return ExprEval.of(len == 0 ? NullHandling.defaultStringValue() : StringUtils.lpad(base, len, pad));
+      }
+
+    }
+  }
+
+  class RpadFunc implements Function
+  {
+    @Override
+    public String name()
+    {
+      return "rpad";
+    }
+
+    @Override
+    public ExprEval apply(List<Expr> args, Expr.ObjectBinding bindings)
+    {
+      if (args.size() != 3) {
+        throw new IAE("Function[%s] needs 3 arguments", name());
+      }
+
+      String base = args.get(0).eval(bindings).asString();
+      int len = args.get(1).eval(bindings).asInt();
+      String pad = args.get(2).eval(bindings).asString();
+
+      if (base == null || pad == null) {
+        return ExprEval.of(null);
+      } else {
+        return ExprEval.of(len == 0 ? NullHandling.defaultStringValue() : StringUtils.rpad(base, len, pad));
+      }
+
+    }
+  }
+
 }

core/src/test/java/org/apache/druid/java/util/common/StringUtilsTest.java

@@ -181,4 +181,43 @@ public class StringUtilsTest
     expectedException.expectMessage("count is negative, -1");
     Assert.assertEquals("", StringUtils.repeat("foo", -1));
   }
+  
+  @Test
+  public void testLpad()
+  {
+    String s1 = StringUtils.lpad("abc", 7, "de");
+    Assert.assertEquals(s1, "dedeabc");
+
+    String s2 = StringUtils.lpad("abc", 6, "de");
+    Assert.assertEquals(s2, "dedabc");
+
+    String s3 = StringUtils.lpad("abc", 2, "de");
+    Assert.assertEquals(s3, "ab");
+
+    String s4 = StringUtils.lpad("abc", 0, "de");
+    Assert.assertEquals(s4, "");
+
+    String s5 = StringUtils.lpad("abc", -1, "de");
+    Assert.assertEquals(s5, null);
+  }
+
+  @Test
+  public void testRpad()
+  {
+    String s1 = StringUtils.rpad("abc", 7, "de");
+    Assert.assertEquals(s1, "abcdede");
+
+    String s2 = StringUtils.rpad("abc", 6, "de");
+    Assert.assertEquals(s2, "abcded");
+
+    String s3 = StringUtils.rpad("abc", 2, "de");
+    Assert.assertEquals(s3, "ab");
+
+    String s4 = StringUtils.rpad("abc", 0, "de");
+    Assert.assertEquals(s4, "");
+
+    String s5 = StringUtils.rpad("abc", -1, "de");
+    Assert.assertEquals(s5, null);
+  }
+
 }

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

@@ -134,4 +134,26 @@ public class FunctionTest
     assertExpr("notnull(null)", 0L);
     assertExpr("notnull('abc')", 1L);
   }
+
+  @Test
+  public void testLpad()
+  {
+    assertExpr("lpad(x, 5, 'ab')", "abfoo");
+    assertExpr("lpad(x, 4, 'ab')", "afoo");
+    assertExpr("lpad(x, 2, 'ab')", "fo");
+    assertExpr("lpad(x, 0, 'ab')", null);
+    assertExpr("lpad(x, 5, null)", null);
+    assertExpr("lpad(null, 5, x)", null);
+  }
+
+  @Test
+  public void testRpad()
+  {
+    assertExpr("rpad(x, 5, 'ab')", "fooab");
+    assertExpr("rpad(x, 4, 'ab')", "fooa");
+    assertExpr("rpad(x, 2, 'ab')", "fo");
+    assertExpr("rpad(x, 0, 'ab')", null);
+    assertExpr("rpad(x, 5, null)", null);
+    assertExpr("rpad(null, 5, x)", null);
+  }
 }

docs/content/misc/math-expr.md

@@ -85,6 +85,8 @@ The following built-in functions are available.
 |upper|upper(expr) converts a string to uppercase|
 |reverse|reverse(expr) reverses a string|
 |repeat|repeat(expr, N) repeats a string N times|
+|lpad|lpad(expr, length, chars) returns a string of `length` from `expr` left-padded with `chars`. If `length` is shorter than the length of `expr`, the result is `expr` which is truncated to `length`. If either `expr` or `chars` are null, the result will be null.|
+|rpad|rpad(expr, length, chars) returns a string of `length` from `expr` right-padded with `chars`. If `length` is shorter than the length of `expr`, the result is `expr` which is truncated to `length`. If either `expr` or `chars` are null, the result will be null.|
 
 ## Time functions
 

docs/content/querying/sql.md

@@ -198,6 +198,9 @@ String functions accept strings, and return a type appropriate to the function.
 |`UPPER(expr)`|Returns expr in all uppercase.|
 |`REVERSE(expr)`|Reverses expr.|
 |`REPEAT(expr, [N])`|Repeats expr N times|
+|`LPAD(expr, length[, chars])`|Returns a string of "length" from "expr" left-padded with "chars". If "length" is shorter than the length of "expr", the result is "expr" which is truncated to "length". If either "expr" or "chars" are null, the result will be null.|
+|`RPAD(expr, length[, chars])`|Returns a string of "length" from "expr" right-padded with "chars". If "length" is shorter than the length of "expr", the result is "expr" which is truncated to "length". If either "expr" or "chars" are null, the result will be null.|
+
 
 ### Time functions
 

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

@@ -0,0 +1,85 @@
+/*
+ * 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.expression.builtin;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.sql.SqlFunction;
+import org.apache.calcite.sql.SqlFunctionCategory;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.OperatorConversions;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.RowSignature;
+
+public class LPadOperatorConversion implements SqlOperatorConversion
+{
+  private static final SqlFunction SQL_FUNCTION = OperatorConversions
+      .operatorBuilder("LPAD")
+      .operandTypes(SqlTypeFamily.CHARACTER, SqlTypeFamily.INTEGER, SqlTypeFamily.CHARACTER)
+      .returnType(SqlTypeName.VARCHAR)
+      .functionCategory(SqlFunctionCategory.STRING)
+      .requiredOperands(2)
+      .build();
+
+  @Override
+  public SqlOperator calciteOperator()
+  {
+    return SQL_FUNCTION;
+  }
+
+  @Override
+  public DruidExpression toDruidExpression(
+      final PlannerContext plannerContext,
+      final RowSignature rowSignature,
+      final RexNode rexNode
+  )
+  {
+    return OperatorConversions.convertCall(
+        plannerContext,
+        rowSignature,
+        rexNode,
+        druidExpressions -> {
+          if (druidExpressions.size() > 2) {
+            return DruidExpression.fromFunctionCall(
+                "lpad",
+                ImmutableList.of(
+                    druidExpressions.get(0),
+                    druidExpressions.get(1),
+                    druidExpressions.get(2)
+                )
+            );
+          } else {
+            return DruidExpression.fromFunctionCall(
+                "lpad",
+                ImmutableList.of(
+                    druidExpressions.get(0),
+                    druidExpressions.get(1),
+                    DruidExpression.fromExpression(DruidExpression.stringLiteral(" "))
+                )
+            );
+          }
+        }
+    );
+  }
+}

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

@@ -0,0 +1,85 @@
+/*
+ * 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.expression.builtin;
+
+import com.google.common.collect.ImmutableList;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.sql.SqlFunction;
+import org.apache.calcite.sql.SqlFunctionCategory;
+import org.apache.calcite.sql.SqlOperator;
+import org.apache.calcite.sql.type.SqlTypeFamily;
+import org.apache.calcite.sql.type.SqlTypeName;
+import org.apache.druid.sql.calcite.expression.DruidExpression;
+import org.apache.druid.sql.calcite.expression.OperatorConversions;
+import org.apache.druid.sql.calcite.expression.SqlOperatorConversion;
+import org.apache.druid.sql.calcite.planner.PlannerContext;
+import org.apache.druid.sql.calcite.table.RowSignature;
+
+public class RPadOperatorConversion implements SqlOperatorConversion
+{
+  private static final SqlFunction SQL_FUNCTION = OperatorConversions
+      .operatorBuilder("RPAD")
+      .operandTypes(SqlTypeFamily.CHARACTER, SqlTypeFamily.INTEGER, SqlTypeFamily.CHARACTER)
+      .returnType(SqlTypeName.VARCHAR)
+      .functionCategory(SqlFunctionCategory.STRING)
+      .requiredOperands(2)
+      .build();
+
+  @Override
+  public SqlOperator calciteOperator()
+  {
+    return SQL_FUNCTION;
+  }
+
+  @Override
+  public DruidExpression toDruidExpression(
+      final PlannerContext plannerContext,
+      final RowSignature rowSignature,
+      final RexNode rexNode
+  )
+  {
+    return OperatorConversions.convertCall(
+        plannerContext,
+        rowSignature,
+        rexNode,
+        druidExpressions -> {
+          if (druidExpressions.size() > 2) {
+            return DruidExpression.fromFunctionCall(
+                "rpad",
+                ImmutableList.of(
+                    druidExpressions.get(0),
+                    druidExpressions.get(1),
+                    druidExpressions.get(2)
+                )
+            );
+          } else {
+            return DruidExpression.fromFunctionCall(
+                "rpad",
+                ImmutableList.of(
+                    druidExpressions.get(0),
+                    druidExpressions.get(1),
+                    DruidExpression.fromExpression(DruidExpression.stringLiteral(" "))
+                )
+            );
+          }
+        }
+    );
+  }
+}

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

@@ -53,12 +53,14 @@ import org.apache.druid.sql.calcite.expression.builtin.ConcatOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.DateTruncOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.ExtractOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.FloorOperatorConversion;
+import org.apache.druid.sql.calcite.expression.builtin.LPadOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.LTrimOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.LeftOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.LikeOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.MillisToTimestampOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.ParseLongOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.PositionOperatorConversion;
+import org.apache.druid.sql.calcite.expression.builtin.RPadOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.RTrimOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.RegexpExtractOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.ReinterpretOperatorConversion;
@@ -196,6 +198,8 @@ public class DruidOperatorTable implements SqlOperatorTable
           .add(new TrimOperatorConversion())
           .add(new TruncateOperatorConversion())
           .add(new AliasedOperatorConversion(new TruncateOperatorConversion(), "TRUNC"))
+          .add(new LPadOperatorConversion())
+          .add(new RPadOperatorConversion())
           // value coercion operators
           .add(new CastOperatorConversion())
           .add(new ReinterpretOperatorConversion())

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

@@ -236,6 +236,43 @@ public class CalciteQueryTest extends BaseCalciteQueryTest
     );
   }
 
+  @Test
+  public void testSelectPadFamily() throws Exception
+  {
+    testQuery(
+        "SELECT\n"
+        + "LPAD('foo', 5, 'x'),\n"
+        + "LPAD('foo', 2, 'x'),\n"
+        + "LPAD('foo', 5),\n"
+        + "RPAD('foo', 5, 'x'),\n"
+        + "RPAD('foo', 2, 'x'),\n"
+        + "RPAD('foo', 5),\n"
+        + "COUNT(*)\n"
+        + "FROM foo",
+        ImmutableList.of(
+            Druids.newTimeseriesQueryBuilder()
+                  .dataSource(CalciteTests.DATASOURCE1)
+                  .intervals(querySegmentSpec(Filtration.eternity()))
+                  .granularity(Granularities.ALL)
+                  .aggregators(aggregators(new CountAggregatorFactory("a0")))
+                  .postAggregators(
+                      expressionPostAgg("p0", "'xxfoo'"),
+                      expressionPostAgg("p1", "'fo'"),
+                      expressionPostAgg("p2", "'  foo'"),
+                      expressionPostAgg("p3", "'fooxx'"),
+                      expressionPostAgg("p4", "'fo'"),
+                      expressionPostAgg("p5", "'foo  '")
+                  )
+                  .context(TIMESERIES_CONTEXT_DEFAULT)
+                  .build()
+        ),
+        ImmutableList.of(
+            new Object[]{"xxfoo", "fo", "  foo", "fooxx", "fo", "foo  ", 6L}
+        )
+    );
+  }
+
+
   @Test
   public void testExplainSelectConstantExpression() throws Exception
   {

sql/src/test/java/org/apache/druid/sql/calcite/expression/ExpressionsTest.java

@@ -42,8 +42,10 @@ import org.apache.druid.math.expr.Parser;
 import org.apache.druid.query.extraction.RegexDimExtractionFn;
 import org.apache.druid.segment.column.ValueType;
 import org.apache.druid.sql.calcite.expression.builtin.DateTruncOperatorConversion;
+import org.apache.druid.sql.calcite.expression.builtin.LPadOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.LeftOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.ParseLongOperatorConversion;
+import org.apache.druid.sql.calcite.expression.builtin.RPadOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.RegexpExtractOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.RepeatOperatorConversion;
 import org.apache.druid.sql.calcite.expression.builtin.ReverseOperatorConversion;
@@ -601,6 +603,33 @@ public class ExpressionsTest extends CalciteTestBase
     );
   }
 
+  @Test
+  public void testPad()
+  {
+    testExpression(
+        rexBuilder.makeCall(
+            new LPadOperatorConversion().calciteOperator(),
+            inputRef("s"),
+            rexBuilder.makeLiteral(5, typeFactory.createSqlType(SqlTypeName.INTEGER), true),
+            rexBuilder.makeLiteral("x")
+        ),
+        DruidExpression.fromExpression("lpad(\"s\",5,'x')"),
+        "xxfoo"
+    );
+
+    testExpression(
+        rexBuilder.makeCall(
+            new RPadOperatorConversion().calciteOperator(),
+            inputRef("s"),
+            rexBuilder.makeLiteral(5, typeFactory.createSqlType(SqlTypeName.INTEGER), true),
+            rexBuilder.makeLiteral("x")
+        ),
+        DruidExpression.fromExpression("rpad(\"s\",5,'x')"),
+        "fooxx"
+    );
+  }
+
+
   @Test
   public void testTimeFloor()
   {