diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/ExpressionNode.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/ExpressionNode.java
index 0742ef2e9..d4e3b697e 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/ExpressionNode.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/ExpressionNode.java
@@ -729,5 +729,9 @@ public class ExpressionNode {
     }    
     return names;
   }
+
+  public boolean isNullSet() {
+    return kind == Kind.Constant && constant == null;
+  }
 		
 }
\ No newline at end of file
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Cell.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Cell.java
index 0e8e37f9a..8e2e07c5e 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Cell.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Cell.java
@@ -13,6 +13,12 @@ public class Cell {
     this.column = column;
   }
   
+  public Cell(Column column, Value value) {
+    super();
+    this.column = column;
+    this.values.add(value);
+  }
+  
   public Column getColumn() {
     return column;
   }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Column.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Column.java
index abddd4664..745e5c99d 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Column.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Column.java
@@ -7,6 +7,7 @@ public class Column {
   private String type;
   private ColumnKind kind;
   private boolean isColl;
+  private boolean duplicateReported;
   
   protected Column() {
     super();
@@ -57,6 +58,42 @@ public class Column {
   public void setColl(boolean isColl) {
     this.isColl = isColl;
   }
+
+  public String diff(Column other) {
+    if (!name.equals(other.name)) {
+      return "Names differ: '"+name+"' vs '"+other.name+"'"; 
+    }
+    if (kind != ColumnKind.Null && other.kind != ColumnKind.Null) {
+      if (length != other.length) {
+        return "Lengths differ: '"+length+"' vs '"+other.length+"'"; 
+      }
+      if (kind != other.kind) {
+        return "Kinds differ: '"+kind+"' vs '"+other.kind+"'"; 
+      }
+      if (isColl != other.isColl) {
+        return "Collection status differs: '"+isColl+"' vs '"+other.isColl+"'"; 
+      }
+    } else if (kind == ColumnKind.Null) {
+      kind = other.kind;
+      length = other.length;
+      isColl = other.isColl;
+    }
+    return null;
+  }
+
+  public boolean isDuplicateReported() {
+    return duplicateReported;
+  }
+
+  public void setDuplicateReported(boolean duplicateReported) {
+    this.duplicateReported = duplicateReported;
+  }
+
+  @Override
+  public String toString() {
+    return "Column [name=" + name + ", length=" + length + ", type=" + type + ", kind=" + kind + ", isColl=" + isColl
+        + "]";
+  }
   
   
 }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/ColumnKind.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/ColumnKind.java
index a1733f1d6..536d2addb 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/ColumnKind.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/ColumnKind.java
@@ -1,5 +1,5 @@
 package org.hl7.fhir.r5.utils.sql;
 
 public enum ColumnKind {
-  String, DateTime, Integer, Decimal, Binary, Time, Boolean, Complex
+  String, DateTime, Integer, Decimal, Binary, Time, Boolean, Complex, Null
 }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Provider.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Provider.java
index d1aeeaabb..9e464a330 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Provider.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Provider.java
@@ -7,5 +7,5 @@ import org.hl7.fhir.r5.model.Base;
 public interface Provider {
   List<Base> fetch(String resourceType);
 
-  Base resolveReference(String ref, String resourceType);
+  Base resolveReference(Base rootResource, String ref, String specifiedResourceType);
 }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Runner.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Runner.java
index 5087a497d..ea4ac1a10 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Runner.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Runner.java
@@ -24,6 +24,7 @@ import org.hl7.fhir.r5.utils.FHIRPathEngine;
 import org.hl7.fhir.r5.utils.FHIRPathEngine.IEvaluationContext;
 import org.hl7.fhir.r5.utils.FHIRPathUtilityClasses.FunctionDetails;
 import org.hl7.fhir.utilities.json.model.JsonObject;
+import org.hl7.fhir.utilities.validation.ValidationMessage;
 
 
 public class Runner implements IEvaluationContext {
@@ -33,9 +34,8 @@ public class Runner implements IEvaluationContext {
   private List<String> prohibitedNames = new ArrayList<String>();
   private FHIRPathEngine fpe;
 
-  private List<Column> columns = new ArrayList<>();
-
   private String resourceName;
+  private List<ValidationMessage> issues;
 
 
   public IWorkerContext getContext() {
@@ -86,15 +86,15 @@ public class Runner implements IEvaluationContext {
     }
     Validator validator = new Validator(context, fpe, prohibitedNames, storage.supportsArrays(), storage.supportsComplexTypes(), storage.needsName());
     validator.checkViewDefinition(path, viewDefinition);
+    issues = validator.getIssues();
     validator.dump();
     validator.check();
     resourceName = validator.getResourceName();
-    columns = validator.getColumns();
     evaluate(viewDefinition);
   }
 
   private void evaluate(JsonObject vd) {
-    Store store = storage.createStore(vd.asString("name"), columns);
+    Store store = storage.createStore(vd.asString("name"), (List<Column>) vd.getUserData("columns"));
 
     List<Base> data = provider.fetch(resourceName);
 
@@ -130,7 +130,20 @@ public class Runner implements IEvaluationContext {
     if (select.has("forEach")) {
       focus.addAll(executeForEach(select, b));
     } else if (select.has("forEachOrNull")) {
+      
       focus.addAll(executeForEachOrNull(select, b));  
+      if (focus.isEmpty()) {
+        List<Column> columns = (List<Column>) select.getUserData("columns");
+        for (List<Cell> row : rows) {
+          for (Column c : columns) {
+            Cell cell = cell(row, c.getName());
+            if (cell == null) {
+              row.add(new Cell(c, null));
+            }
+          }
+        }
+        return;
+      }
     } else {
       focus.add(b);
     }
@@ -149,19 +162,30 @@ public class Runner implements IEvaluationContext {
         executeColumn(column, f, rowsToAdd);
       }
 
-      for (JsonObject sub : select.getJsonObjects("unionAll")) {
-        executeSelect(sub, f, rowsToAdd);
-      }
-      
       for (JsonObject sub : select.getJsonObjects("select")) {
         executeSelect(sub, f, rowsToAdd);
       }
+      
+      executeUnionAll(select.getJsonObjects("unionAll"), f, rowsToAdd);
+      
       rows.addAll(rowsToAdd);
     }
   }
 
-  private List<Base> executeUnion(JsonObject focus,  Base b, List<List<Cell>> rows) {
-    throw new FHIRException("union is not supported");   
+  private void executeUnionAll(List<JsonObject> unionList,  Base b, List<List<Cell>> rows) {
+    if (unionList.isEmpty()) {
+      return;
+    }
+    List<List<Cell>> sourceRows = new ArrayList<>();
+    sourceRows.addAll(rows);
+    rows.clear();
+
+    for (JsonObject union : unionList) {
+      List<List<Cell>> tempRows = new ArrayList<>();
+      tempRows.addAll(sourceRows);      
+      executeSelect(union, b, tempRows);
+      rows.addAll(tempRows);
+    }
   }
 
   private List<List<Cell>> cloneRows(List<List<Cell>> rows) {
@@ -191,9 +215,6 @@ public class Runner implements IEvaluationContext {
     ExpressionNode n = (ExpressionNode) focus.getUserData("forEachOrNull");
     List<Base> result = new ArrayList<>();
     result.addAll(fpe.evaluate(b, n));
-    if (result.size() == 0) {
-      result.add(null);
-    }
     return result;  
   }
 
@@ -203,23 +224,27 @@ public class Runner implements IEvaluationContext {
     if (b != null) {
       bl2.addAll(fpe.evaluate(b, n));
     }
-    String name = column.getUserString("name");
-    for (List<Cell> row : rows) {
-      Cell c = cell(row, name);
-      if (c == null) {
-        c = new Cell(column(name));
-        row.add(c);
-      }      
-      if (!bl2.isEmpty()) {
-        if (bl2.size() + c.getValues().size() > 1) {
-          // this is a problem if collection != true or if the storage can't deal with it 
-          // though this should've been picked up before now - but there are circumstances where it wouldn't be
-          if (!c.getColumn().isColl()) {
-            throw new FHIRException("The column "+c.getColumn().getName()+" is not allowed multiple values, but at least one row has multiple values");
+    Column col = (Column) column.getUserData("column");
+    if (col == null) {
+      System.out.println("Error");
+    } else {
+      for (List<Cell> row : rows) {
+        Cell c = cell(row, col.getName());
+        if (c == null) {
+          c = new Cell(col);
+          row.add(c);
+        }      
+        if (!bl2.isEmpty()) {
+          if (bl2.size() + c.getValues().size() > 1) {
+            // this is a problem if collection != true or if the storage can't deal with it 
+            // though this should've been picked up before now - but there are circumstances where it wouldn't be
+            if (!c.getColumn().isColl()) {
+              throw new FHIRException("The column "+c.getColumn().getName()+" is not allowed multiple values, but at least one row has multiple values");
+            }
+          }
+          for (Base b2 : bl2) {
+            c.getValues().add(genValue(c.getColumn(), b2));
           }
-        }
-        for (Base b2 : bl2) {
-          c.getValues().add(genValue(c.getColumn(), b2));
         }
       }
     }
@@ -299,7 +324,7 @@ public class Runner implements IEvaluationContext {
     }
   }
   
-  private Column column(String columnName) {
+  private Column column(String columnName, List<Column> columns) {
     for (Column t : columns) {
       if (t.getName().equalsIgnoreCase(columnName)) {
         return t;
@@ -353,7 +378,7 @@ public class Runner implements IEvaluationContext {
   public List<Base> executeFunction(FHIRPathEngine engine, Object appContext, List<Base> focus, String functionName, List<List<Base>> parameters) {
     switch (functionName) {
     case "getResourceKey" : return executeResourceKey(focus);
-    case "getReferenceKey" : return executeReferenceKey(focus, parameters);
+    case "getReferenceKey" : return executeReferenceKey(null, focus, parameters);
     default: throw new Error("Not known: "+functionName);
     }
   }
@@ -375,7 +400,7 @@ public class Runner implements IEvaluationContext {
     return base;
   }
   
-  private List<Base> executeReferenceKey(List<Base> focus, List<List<Base>> parameters) {
+  private List<Base> executeReferenceKey(Base rootResource, List<Base> focus, List<List<Base>> parameters) {
     String rt = null;
     if (parameters.size() > 0) {
       rt = parameters.get(0).get(0).primitiveValue();
@@ -395,7 +420,7 @@ public class Runner implements IEvaluationContext {
         throw new FHIRException("Unable to generate a reference key based on a "+res.fhirType());
       }
       if (ref !=  null) {
-        Base target = provider.resolveReference(ref, rt);
+        Base target = provider.resolveReference(rootResource, ref, rt);
         if (target != null) {
           if (!res.hasUserData("Storage.key")) {
             String key = storage.getKeyForTargetResource(target);
@@ -437,6 +462,9 @@ public class Runner implements IEvaluationContext {
   public boolean paramIsType(String name, int index) {
     return "getReferenceKey".equals(name);
   }
+  public List<ValidationMessage> getIssues() {
+    return issues;
+  }
 
 
 }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageJson.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageJson.java
index 9aca2cb22..d0e3aaeed 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageJson.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageJson.java
@@ -48,7 +48,9 @@ public class StorageJson implements Storage {
   }
 
   private JsonElement makeJsonNode(Value value) {
-    if (value.getValueInt() != null) {
+    if (value == null) {
+      return new JsonNull();
+    } else if (value.getValueInt() != null) {
       return new JsonNumber(value.getValueInt().intValue());
     }
     if (value.getValueBoolean() != null) {
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageSqlite3.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageSqlite3.java
index 0332e17fd..1a32d9c46 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageSqlite3.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/StorageSqlite3.java
@@ -2,6 +2,7 @@ package org.hl7.fhir.r5.utils.sql;
 
 import java.sql.Connection;
 import java.sql.PreparedStatement;
+import java.sql.SQLType;
 import java.util.List;
 
 import org.hl7.fhir.exceptions.FHIRException;
@@ -27,7 +28,7 @@ public class StorageSqlite3 implements Storage {
   private Connection conn;
   private int nextKey = 0;
   
-  protected StorageSqlite3(Connection conn) {
+  public StorageSqlite3(Connection conn) {
     super();
     this.conn = conn;
   }
@@ -38,7 +39,7 @@ public class StorageSqlite3 implements Storage {
       CommaSeparatedStringBuilder fields = new CommaSeparatedStringBuilder(", ");
       CommaSeparatedStringBuilder values = new CommaSeparatedStringBuilder(", ");
       StringBuilder b = new StringBuilder();
-      b.append("Create Table "+name+" { ");
+      b.append("Create Table "+name+" ( ");
       b.append("ViewRowKey integer NOT NULL");
       for (Column column : columns) {
         b.append(", "+column.getName()+" "+sqliteType(column.getKind())+" NULL"); // index columns are always nullable
@@ -48,7 +49,7 @@ public class StorageSqlite3 implements Storage {
       b.append(", PRIMARY KEY (ViewRowKey))\r\n");
       conn.createStatement().execute(b.toString());
 
-      String isql = "Insert into "+name+" ("+fields.toString()+") values ("+values.toString()+")";
+      String isql = "Insert into "+name+" (ViewRowKey, "+fields.toString()+") values (?, "+values.toString()+")";
       PreparedStatement psql = conn.prepareStatement(isql);
       return new SQLiteStore(name, psql);
     } catch (Exception e) {
@@ -79,6 +80,8 @@ public class StorageSqlite3 implements Storage {
       for (int i = 0; i < cells.size(); i++) {
         Cell c = cells.get(i);
         switch (c.getColumn().getKind()) {
+        case Null: 
+          p.setNull(i+2, java.sql.Types.NVARCHAR);
         case Binary:
           p.setBytes(i+2, c.getValues().size() == 0 ? null : c.getValues().get(0).getValueBinary());
           break;
@@ -103,6 +106,7 @@ public class StorageSqlite3 implements Storage {
         case Complex: throw new FHIRException("SQLite runner does not handle complexes");
         }
       }
+      p.execute();
     } catch (Exception e) {
       throw new FHIRException(e);
     }
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Validator.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Validator.java
index 7aa5cc8f9..c2dbd1b54 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Validator.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/sql/Validator.java
@@ -18,6 +18,7 @@ import org.hl7.fhir.utilities.json.model.JsonBoolean;
 import org.hl7.fhir.utilities.json.model.JsonElement;
 import org.hl7.fhir.utilities.json.model.JsonNumber;
 import org.hl7.fhir.utilities.json.model.JsonObject;
+import org.hl7.fhir.utilities.json.model.JsonProperty;
 import org.hl7.fhir.utilities.json.model.JsonString;
 import org.hl7.fhir.utilities.validation.ValidationMessage;
 import org.hl7.fhir.utilities.validation.ValidationMessage.IssueSeverity;
@@ -35,7 +36,6 @@ public class Validator {
   private Boolean needsName;
 
   private String resourceName;
-  private List<Column> columns = new ArrayList<Column>();
   private String name;
 
   public Validator(IWorkerContext context, FHIRPathEngine fpe, List<String> prohibitedNames, Boolean arrays, Boolean complexTypes, Boolean needsName) {
@@ -52,11 +52,10 @@ public class Validator {
     return resourceName;
   }
 
-  public List<Column> getColumns() {
-    return columns;
-  }
 
-  public void checkViewDefinition(String path, JsonObject viewDefinition) {
+  public void checkViewDefinition(String path, JsonObject viewDefinition) {    
+    checkProperties(viewDefinition, path, "url", "identifier", "name", "version", "title", "status", "experimental", "date", "publisher", "contact", "description", "useContext", "copyright", "resource", "constant", "select", "where");
+    
     JsonElement nameJ = viewDefinition.get("name");
     if (nameJ == null) {
       if (needsName == null) {
@@ -76,9 +75,12 @@ public class Validator {
       }
     }
 
+    List<Column> columns = new ArrayList<>();    
+    viewDefinition.setUserData("columns", columns);
+    
     JsonElement resourceNameJ = viewDefinition.get("resource");
     if (resourceNameJ == null) {
-      error(path, viewDefinition, "No resource provided", IssueType.REQUIRED);      
+      error(path, viewDefinition, "No resource specified", IssueType.REQUIRED);      
     } else if (!(resourceNameJ instanceof JsonString)) {
       error(path, viewDefinition, "resource must be a string", IssueType.INVALID);      
     } else {
@@ -102,29 +104,24 @@ public class Validator {
         }
         TypeDetails t = new TypeDetails(CollectionStatus.SINGLETON, resourceName);
 
-        if (viewDefinition.has("forEach")) {
-          checkForEach(path, viewDefinition, viewDefinition.get("forEach"), t);
-        } else if (viewDefinition.has("forEachOrNull")) {
-          checkForEachOrNull(path, viewDefinition, viewDefinition.get("forEachOrNull"), t);
-        } else if (viewDefinition.has("unionAll")) {
-          checkUnion(path, viewDefinition, viewDefinition.get("unionAll"), t);
-        } else {
-          i = 0;
-          if (checkAllObjects(path, viewDefinition, "select")) {
-            for (JsonObject select : viewDefinition.getJsonObjects("select")) {
-              checkSelect(path+".select["+i+"]", select, t);
-              i++;
-            }
-            if (i == 0) {
-              error(path, viewDefinition, "No select statements found", IssueType.REQUIRED);
-            }
+        i = 0;
+        if (checkAllObjects(path, viewDefinition, "select")) {
+          for (JsonObject select : viewDefinition.getJsonObjects("select")) {
+            columns.addAll(checkSelect(path+".select["+i+"]", select, t));
+            i++;
+          }
+          if (i == 0) {
+            error(path, viewDefinition, "No select statements found", IssueType.REQUIRED);
           }
         }
       }
     }
   }
 
-  private void checkSelect(String path, JsonObject select, TypeDetails t) {
+  private List<Column> checkSelect(String path, JsonObject select, TypeDetails t) {
+    List<Column> columns = new ArrayList<>();
+    select.setUserData("columns", columns);
+    checkProperties(select, path, "column", "select", "forEach", "forEachOrNull", "unionAll");
 
     if (select.has("forEach")) {
       t = checkForEach(path, select, select.get("forEach"), t);
@@ -133,24 +130,18 @@ public class Validator {
     } 
 
     if (t != null) {
-      boolean content = false;
-
-      if (select.has("unionAll")) {
-        content = checkUnion(path, select, select.get("unionAll"), t);
-      } 
       
       if (select.has("column")) {
         JsonElement a = select.get("column");
         if (!(a instanceof JsonArray)) {
           error(path+".column", a, "column is not an array", IssueType.INVALID);
         } else {
-          content = true;
           int i = 0;
           for (JsonElement e : ((JsonArray) a)) {
             if (!(e instanceof JsonObject)) {
               error(path+".column["+i+"]", a, "column["+i+"] is a "+e.type().toName()+" not an object", IssueType.INVALID);
             } else { 
-              checkColumn(path+".column["+i+"]", (JsonObject) e, t);
+              columns.add(checkColumn(path+".column["+i+"]", (JsonObject) e, t));
             }
           }      
         }     
@@ -161,47 +152,98 @@ public class Validator {
         if (!(a instanceof JsonArray)) {
           error(path+".select", a, "select is not an array", IssueType.INVALID);
         } else {
-          content = true;
           int i = 0;
           for (JsonElement e : ((JsonArray) a)) {
             if (!(e instanceof JsonObject)) {
               error(path+".select["+i+"]", e, "select["+i+"] is not an object", IssueType.INVALID);
             } else { 
-              checkSelect(path+".select["+i+"]", (JsonObject) e, t);
+              columns.addAll(checkSelect(path+".select["+i+"]", (JsonObject) e, t));
             }
           }      
         }     
       }
 
-      if (!content) {
+      if (select.has("unionAll")) {
+        columns.addAll(checkUnion(path, select, select.get("unionAll"), t));
+      } 
+      if (columns.isEmpty()) {
         error(path, select, "The select has no columns or selects", IssueType.REQUIRED);
+      } else {
+        checkColumnNamesUnique(select, path, columns);
       }
     }
+    return columns;
   }
 
 
-  private boolean checkUnion(String path, JsonObject focus, JsonElement expression,  TypeDetails t) {
+  private void checkColumnNamesUnique(JsonObject select, String path, List<Column> columns) {
+    Set<String> names = new HashSet<>();
+    for (Column col : columns) {
+      if (col != null) {
+        if (!names.contains(col.getName())) {
+          names.add(col.getName());       
+        } else if (!col.isDuplicateReported()) {
+          col.setDuplicateReported(true);
+          error(path, select, "Duplicate Column Name '"+col.getName()+"'", IssueType.BUSINESSRULE);
+        }
+      }
+    }    
+  }
+
+  private List<Column> checkUnion(String path, JsonObject focus, JsonElement expression,  TypeDetails t) {
     JsonElement a = focus.get("unionAll");
     if (!(a instanceof JsonArray)) {
-      error(path+".union", a, "union is not an array", IssueType.INVALID);
-      return false;
-    } else {      
+      error(path+".unionAll", a, "union is not an array", IssueType.INVALID);
+      return null;
+    } else {  
+      List<List<Column>> unionColumns = new ArrayList<>();
       int i = 0;
       for (JsonElement e : ((JsonArray) a)) {
         if (!(e instanceof JsonObject)) {
-          error(path+".union["+i+"]", e, "union["+i+"] is not an object", IssueType.INVALID);
+          error(path+".unionAll["+i+"]", e, "unionAll["+i+"] is not an object", IssueType.INVALID);
         } else { 
-          checkSelect(path+".union["+i+"]", (JsonObject) e, t);
+          unionColumns.add(checkSelect(path+".unionAll["+i+"]", (JsonObject) e, t));
         }
+        i++;
       }  
       if (i < 2) {
-        warning(path+".union", a, "union should have more than one item");        
+        warning(path+".unionAll", a, "unionAll should have more than one item");        
+      }
+      if (unionColumns.size() > 1) {
+        List<Column> columns = unionColumns.get(0);
+        for (int ic = 1; ic < unionColumns.size(); ic++) {
+          String diff = columnDiffs(columns, unionColumns.get(ic));
+          if (diff != null) {
+            error(path+".unionAll["+i+"]", ((JsonArray) a).get(ic), "unionAll["+i+"] column definitions do not match: "+diff, IssueType.INVALID);            
+          }
+        }
+        a.setUserData("colunms", columns);
+        return columns;
       }
-      return true;
     }     
+    return null;
   }
   
-  private void checkColumn(String path, JsonObject column, TypeDetails t) {
+  private String columnDiffs(List<Column> list1, List<Column> list2) {
+    if (list1.size() == list2.size()) {
+      for (int i = 0; i < list1.size(); i++) {
+        if (list1.get(i) == null || list2.get(i) == null) {
+          return null; // just suppress any addition errors
+        }
+        String diff = list1.get(i).diff(list2.get(i));
+        if (diff != null) {
+          return diff+" at #"+i;
+        }
+      }
+      return null;
+    } else {
+      return "Column counts differ: "+list1.size()+" vs "+list2.size();
+    }
+  }
+
+  private Column checkColumn(String path, JsonObject column, TypeDetails t) {
+    checkProperties(column, path, "path", "name", "description", "collection", "type", "tag");
+
     if (!column.has("path")) {
       error(path, column, "no path found", IssueType.INVALID);      
     } else {
@@ -253,7 +295,7 @@ public class Validator {
           // ok, name is sorted!
           if (columnName != null) {
             column.setUserData("name", columnName);
-            boolean isColl = (td.getCollectionStatus() != CollectionStatus.SINGLETON) || column(columnName) != null;
+            boolean isColl = (td.getCollectionStatus() != CollectionStatus.SINGLETON);
             if (column.has("collection")) {
               JsonElement collectionJ = column.get("collection");
               if (!(collectionJ instanceof JsonBoolean)) {
@@ -273,24 +315,28 @@ public class Validator {
                 warning(path, expression, "column appears to be a collection, but this is not allowed in this context");
               }
             }
-            // ok collection is sorted
             Set<String> types = new HashSet<>();
-            for (String type : td.getTypes()) {
-              types.add(simpleType(type));
-            }
+            if (node.isNullSet()) {
+              types.add("null");
+            } else {
+              // ok collection is sorted
+              for (String type : td.getTypes()) {
+                types.add(simpleType(type));
+              }
 
-            JsonElement typeJ = column.get("type");
-            if (typeJ != null) {
-              if (typeJ instanceof JsonString) {
-                String type = typeJ.asString();
-                if (!td.hasType(type)) {
-                  error(path+".type", typeJ, "The path expression does not return a value of the type '"+type, IssueType.VALUE);
+              JsonElement typeJ = column.get("type");
+              if (typeJ != null) {
+                if (typeJ instanceof JsonString) {
+                  String type = typeJ.asString();
+                  if (!td.hasType(type)) {
+                    error(path+".type", typeJ, "The path expression does not return a value of the type '"+type, IssueType.VALUE);
+                  } else {
+                    types.clear();
+                    types.add(simpleType(type));
+                  }
                 } else {
-                  types.clear();
-                  types.add(simpleType(type));
+                  error(path+".type", typeJ, "type must be a string", IssueType.INVALID);
                 }
-              } else {
-                error(path+".type", typeJ, "type must be a string", IssueType.INVALID);
               }
             }
             if (types.size() != 1) {
@@ -298,7 +344,7 @@ public class Validator {
             } else {
               String type = types.iterator().next();
               boolean ok = false;
-              if (!isSimpleType(type)) {
+              if (!isSimpleType(type) && !"null".equals(type)) {
                 if (complexTypes) {
                   warning(path, expression, "Column is a complex type. This is not supported in some Runners");
                 } else if (!complexTypes) {            
@@ -310,28 +356,21 @@ public class Validator {
                 ok = true;
               }
               if (ok) {
-                Column col = column(columnName);
-                if (col != null) {
-                  if (!col.getType().equals(type)) {
-                    error(path, expression, "Duplicate definition for "+columnName+" has different types ("+col.getType()+" vs "+type+")", IssueType.BUSINESSRULE);
-                  }
-                  if (col.isColl() != isColl) {
-                    error(path, expression, "Duplicate definition for "+columnName+" has different status for collection ("+col.isColl()+" vs "+isColl+")", IssueType.BUSINESSRULE);
-                  }
-                } else {
-                  columns.add(new Column(columnName, isColl, type, kindForType(type)));
-
-                }
+                Column col = new Column(columnName, isColl, type, kindForType(type));
+                column.setUserData("column", col);
+                return col;
               }
             }
           }
         }
       }
     }
+    return null;
   }
 
   private ColumnKind kindForType(String type) {
     switch (type) {
+    case "null": return ColumnKind.Null;
     case "dateTime": return ColumnKind.DateTime;
     case "boolean": return ColumnKind.Boolean;
     case "integer": return ColumnKind.Integer;
@@ -343,15 +382,6 @@ public class Validator {
     }
   }
 
-  private Column column(String columnName) {
-    for (Column t : columns) {
-      if (t.getName().equalsIgnoreCase(columnName)) {
-        return t;
-      }
-    }
-    return null;
-  }
-
   private boolean isSimpleType(String type) {
     return Utilities.existsInList(type, "dateTime", "boolean", "integer", "decimal", "string", "base64Binary");
   }
@@ -433,6 +463,7 @@ public class Validator {
   }
 
   private void checkConstant(String path, JsonObject constant) {
+    checkProperties(constant, path, "name", "valueBase64Binary", "valueBoolean", "valueCanonical", "valueCode", "valueDate", "valueDateTime", "valueDecimal", "valueId", "valueInstant", "valueInteger", "valueInteger64", "valueOid", "valueString", "valuePositiveInt", "valueTime", "valueUnsignedInt", "valueUri", "valueUrl", "valueUuid");
     JsonElement nameJ = constant.get("name");
     if (nameJ == null) {
       error(path, constant, "No name provided", IssueType.REQUIRED);      
@@ -508,6 +539,8 @@ public class Validator {
     }
   }
   private void checkWhere(String path, JsonObject where) {
+    checkProperties(where, path, "path", "description");
+
     String expr = where.asString("path");
     if (expr == null) {
       error(path, where, "No path provided", IssueType.REQUIRED);
@@ -534,6 +567,19 @@ public class Validator {
     }
   }
 
+  private void checkProperties(JsonObject obj, String path, String... names) {
+    for (JsonProperty p : obj.getProperties()) {
+      boolean nameOk = "extension".equals(p.getName());
+      for (String name : names) {
+        nameOk = nameOk || name.equals(p.getName());
+      }
+      if (!nameOk) {
+        error(path+"."+p.getName(), p.getValue(), "Unknown JSON "+p.getValue().type().name(), IssueType.UNKNOWN);
+      }
+    }
+    
+  }
+
   private boolean isValidName(String name) {
     boolean first = true;
     for (char c : name.toCharArray()) {
diff --git a/org.hl7.fhir.r5/src/test/java/org/hl7/fhir/r5/sql/SQLOnFhirTests.java b/org.hl7.fhir.r5/src/test/java/org/hl7/fhir/r5/sql/SQLOnFhirTests.java
index 74daafaec..e0bf364e9 100644
--- a/org.hl7.fhir.r5/src/test/java/org/hl7/fhir/r5/sql/SQLOnFhirTests.java
+++ b/org.hl7.fhir.r5/src/test/java/org/hl7/fhir/r5/sql/SQLOnFhirTests.java
@@ -54,7 +54,7 @@ public class SQLOnFhirTests {
     }
 
     @Override
-    public Base resolveReference(String ref, String rt) {
+    public Base resolveReference(Base rootResource, String ref, String rt) {
       if (ref == null) {
         return null;
       }
@@ -109,7 +109,7 @@ public class SQLOnFhirTests {
   @SuppressWarnings("deprecation")
   @ParameterizedTest(name = "{index}: file {0}")
   @MethodSource("data")
-  @Disabled
+  //@Disabled
   public void test(String name, TestDetails test) throws FileNotFoundException, IOException, FHIRException, org.hl7.fhir.exceptions.FHIRException, UcumException {
     this.details = test;
     Runner runner = new Runner();
@@ -126,6 +126,7 @@ public class SQLOnFhirTests {
       runner.execute(test.path+".view", test.testCase.getJsonObject("view"));
       results = store.getRows();
     } catch (Exception e) {
+      e.printStackTrace();
       Assertions.assertTrue(test.testCase.has("expectError"), e.getMessage());
     }
     if (results != null) {