Fix GROUP BY with two identical columns in selected expressions

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

@@ -108,6 +108,9 @@ public class Select extends Query {
     SelectGroups groupData;
 
     private int havingIndex;
+
+    private int[] groupByCopies;
+
     boolean isGroupQuery;
     private boolean isGroupSortedQuery;
     private boolean isWindowQuery;
@@ -462,7 +465,8 @@ public class Select extends Query {
 
     void updateAgg(int columnCount, int stage) {
         for (int i = 0; i < columnCount; i++) {
-            if (groupByExpression == null || !groupByExpression[i]) {
+            if ((groupByExpression == null || !groupByExpression[i])
+                    && (groupByCopies == null || groupByCopies[i] < 0)) {
                 Expression expr = expressions.get(i);
                 expr.updateAggregate(session, stage);
             }
@@ -480,6 +484,13 @@ public class Select extends Query {
                 if (groupByExpression != null && groupByExpression[j]) {
                     continue;
                 }
+                if (groupByCopies != null) {
+                    int original = groupByCopies[j];
+                    if (original >= 0) {
+                        row[j] = row[original];
+                        continue;
+                    }
+                }
                 Expression expr = expressions.get(j);
                 row[j] = expr.getValue(session);
             }
@@ -1047,7 +1058,7 @@ public class Select extends Query {
                 for (int j = 0; j < expSize; j++) {
                     String s2 = expressionSQL.get(j);
                     if (db.equalsIdentifiers(s2, sql)) {
-                        found = j;
+                        found = mergeGroupByExpressions(db, j, expressionSQL, false);
                         break;
                     }
                 }
@@ -1056,12 +1067,12 @@ public class Select extends Query {
                     for (int j = 0; j < expSize; j++) {
                         Expression e = expressions.get(j);
                         if (db.equalsIdentifiers(sql, e.getAlias())) {
-                            found = j;
+                            found = mergeGroupByExpressions(db, j, expressionSQL, true);
                             break;
                         }
                         sql = expr.getAlias();
                         if (db.equalsIdentifiers(sql, e.getAlias())) {
-                            found = j;
+                            found = mergeGroupByExpressions(db, j, expressionSQL, true);
                             break;
                         }
                     }
@@ -1074,6 +1085,14 @@ public class Select extends Query {
                     groupIndex[i] = found;
                 }
             }
+            checkUsed: if (groupByCopies != null) {
+                for (int i : groupByCopies) {
+                    if (i >= 0) {
+                        break checkUsed;
+                    }
+                }
+                groupByCopies = null;
+            }
             groupByExpression = new boolean[expressions.size()];
             for (int gi : groupIndex) {
                 groupByExpression[gi] = true;
@@ -1092,6 +1111,50 @@ public class Select extends Query {
         checkInit = true;
     }
 
+    private int mergeGroupByExpressions(Database db, int index, ArrayList<String> expressionSQL, boolean scanPrevious)
+    {
+        /*
+         * -1: uniqueness of expression is not known yet
+         *
+         * -2: expression that is used as a source for a copy or does not have
+         * copies
+         *
+         * >=0: expression is a copy of expression at this index
+         */
+        if (groupByCopies != null) {
+            int c = groupByCopies[index];
+            if (c >= 0) {
+                return c;
+            } else if (c == -2) {
+                return index;
+            }
+        } else {
+            groupByCopies = new int[expressionSQL.size()];
+            Arrays.fill(groupByCopies, -1);
+        }
+        String sql = expressionSQL.get(index);
+        if (scanPrevious) {
+            /*
+             * If expression was matched using an alias previous expressions may
+             * be identical.
+             */
+            for (int i = 0; i < index; i++) {
+                if (db.equalsIdentifiers(sql, expressionSQL.get(i))) {
+                    index = i;
+                    break;
+                }
+            }
+        }
+        int l = expressionSQL.size();
+        for (int i = index + 1; i < l; i++) {
+            if (db.equalsIdentifiers(sql, expressionSQL.get(i))) {
+                groupByCopies[i] = index;
+            }
+        }
+        groupByCopies[index] = -2;
+        return index;
+    }
+
     @Override
     public void prepare() {
         if (isPrepared) {

h2/src/test/org/h2/test/scripts/dml/select.sql

@@ -466,3 +466,46 @@ DROP TABLE TEST;
 
 SELECT 1 = ALL (SELECT * FROM VALUES (NULL), (1), (2), (NULL) ORDER BY 1);
 >> FALSE
+
+CREATE TABLE TEST(G INT, V INT);
+> ok
+
+INSERT INTO TEST VALUES (10, 1), (11, 2), (20, 4);
+> update count: 3
+
+SELECT G / 10 G1, G / 10 G2, SUM(T.V) S FROM TEST T GROUP BY G / 10, G / 10;
+> G1 G2 S
+> -- -- -
+> 1  1  3
+> 2  2  4
+> rows: 2
+
+
+SELECT G / 10 G1, G / 10 G2, SUM(T.V) S FROM TEST T GROUP BY G2;
+> G1 G2 S
+> -- -- -
+> 1  1  3
+> 2  2  4
+> rows: 2
+
+DROP TABLE TEST;
+> ok
+
+@reconnect off
+
+CALL RAND(0);
+>> 0.730967787376657
+
+SELECT RAND(), RAND() + 1, RAND() + 1, RAND() GROUP BY RAND() + 1;
+> RAND()             RAND() + 1         RAND() + 1         RAND()
+> ------------------ ------------------ ------------------ ------------------
+> 0.6374174253501083 1.2405364156714858 1.2405364156714858 0.5504370051176339
+> rows: 1
+
+SELECT RAND() A, RAND() + 1 B, RAND() + 1 C, RAND() D, RAND() + 2 E, RAND() + 3 F GROUP BY B, C, E, F;
+> A                  B                  C                  D                  E                  F
+> ------------------ ------------------ ------------------ ------------------ ------------------ ------------------
+> 0.8791825178724801 1.3332183994766498 1.3332183994766498 0.9412491794821144 2.3851891847407183 3.9848415401998087
+> rows: 1
+
+@reconnect on