Allow expressions based on DISTINCT values in ORDER BY

h2/src/main/org/h2/command/dml/Query.java

@@ -14,9 +14,14 @@ import org.h2.engine.Database;
 import org.h2.engine.Session;
 import org.h2.engine.Mode.ModeEnum;
 import org.h2.expression.Alias;
+import org.h2.expression.Comparison;
+import org.h2.expression.ConditionAndOr;
+import org.h2.expression.ConditionNot;
 import org.h2.expression.Expression;
 import org.h2.expression.ExpressionColumn;
 import org.h2.expression.ExpressionVisitor;
+import org.h2.expression.Function;
+import org.h2.expression.Operation;
 import org.h2.expression.Parameter;
 import org.h2.expression.ValueExpression;
 import org.h2.message.DbException;
@@ -480,7 +485,9 @@ public abstract class Query extends Prepared {
             if (!isAlias) {
                 if (mustBeInResult) {
                     if (session.getDatabase().getMode().getEnum() != ModeEnum.MySQL) {
-                        throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT, e.getSQL());
+                        if (!checkOrderOther(session, e, expressionSQL)) {
+                            throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT, e.getSQL());
+                        }
                     }
                 }
                 expressions.add(e);
@@ -492,6 +499,52 @@ public abstract class Query extends Prepared {
         }
     }
 
+    private static boolean checkOrderOther(Session session, Expression expr, ArrayList<String> expressionSQL) {
+        if (expr.isConstant()) {
+            return true;
+        }
+        if (expressionSQL != null) {
+            String exprSQL = expr.getSQL();
+            for (String sql: expressionSQL) {
+                if (session.getDatabase().equalsIdentifiers(exprSQL, sql)) {
+                    return true;
+                }
+            }
+        }
+        if (expr instanceof Function) {
+            Function function = (Function) expr;
+            if (!function.isDeterministic()) {
+                return false;
+            }
+            for (Expression e : function.getArgs()) {
+                if (!checkOrderOther(session, e, expressionSQL)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+        if (expr instanceof Operation) {
+            Operation operation = (Operation) expr;
+            Expression right = operation.getExpression(false);
+            return checkOrderOther(session, operation.getExpression(true), expressionSQL)
+                    && (right == null || checkOrderOther(session, right, expressionSQL));
+        }
+        if (expr instanceof ConditionAndOr) {
+            ConditionAndOr condition = (ConditionAndOr) expr;
+            return checkOrderOther(session, condition.getExpression(true), expressionSQL)
+                    && checkOrderOther(session, condition.getExpression(false), expressionSQL);
+        }
+        if (expr instanceof ConditionNot) {
+            return checkOrderOther(session, ((ConditionNot) expr).getCondition(), expressionSQL);
+        }
+        if (expr instanceof Comparison) {
+            Comparison condition = (Comparison) expr;
+            return checkOrderOther(session, condition.getExpression(true), expressionSQL)
+                    && checkOrderOther(session, condition.getExpression(false), expressionSQL);
+        }
+        return false;
+    }
+
     /**
      * Create a {@link SortOrder} object given the list of {@link SelectOrderBy}
      * objects. The expression list is extended if necessary.

h2/src/main/org/h2/expression/ConditionNot.java

@@ -98,4 +98,13 @@ public class ConditionNot extends Condition {
         return condition.getCost();
     }
 
+    /**
+     * Get the sub-expression of this condition.
+     *
+     * @return the sub-expression
+     */
+    public Expression getCondition() {
+        return condition;
+    }
+
 }

h2/src/main/org/h2/expression/Operation.java

@@ -407,4 +407,15 @@ public class Operation extends Expression {
         return left.getCost() + 1 + (right == null ? 0 : right.getCost());
     }
 
+    /**
+     * Get the left or the right sub-expression of this condition.
+     *
+     * @param getLeft true to get the left sub-expression, false to get the
+     *            right sub-expression.
+     * @return the sub-expression
+     */
+    public Expression getExpression(boolean getLeft) {
+        return getLeft ? this.left : right;
+    }
+
 }

h2/src/test/org/h2/test/scripts/distinct.sql

@@ -15,6 +15,60 @@ CREATE TABLE TEST2(ID2 BIGINT);
 INSERT INTO TEST2 VALUES (1), (2);
 > update count: 2
 
+SELECT DISTINCT NAME FROM TEST ORDER BY NAME;
+> NAME
+> ----
+> B
+> a
+> c
+> rows (ordered): 3
+
+SELECT DISTINCT NAME FROM TEST ORDER BY LOWER(NAME);
+> NAME
+> ----
+> a
+> B
+> c
+> rows (ordered): 3
+
+SELECT DISTINCT ID FROM TEST ORDER BY ID;
+> ID
+> --
+> 1
+> 2
+> 3
+> rows (ordered): 3
+
+SELECT DISTINCT ID FROM TEST ORDER BY -ID - 1;
+> ID
+> --
+> 3
+> 2
+> 1
+> rows (ordered): 3
+
+SELECT DISTINCT ID FROM TEST ORDER BY (-ID + 10) > 0 AND NOT (ID = 0), ID;
+> ID
+> --
+> 1
+> 2
+> 3
+> rows (ordered): 3
+
+SELECT DISTINCT NAME, ID + 1 FROM TEST ORDER BY UPPER(NAME) || (ID + 1);
+> NAME ID + 1
+> ---- ------
+> a    2
+> B    3
+> c    4
+> rows (ordered): 3
+
+SELECT DISTINCT ID FROM TEST ORDER BY NAME;
+> exception ORDER_BY_NOT_IN_RESULT
+
+SELECT DISTINCT ID FROM TEST ORDER BY CURRENT_TIMESTAMP;
+> exception ORDER_BY_NOT_IN_RESULT
+
 SET MODE MySQL;
 > ok