fix userSetElement In Gropby

src/common/backend/parser/parse_clause.cpp

@@ -1908,6 +1908,12 @@ static Index transformGroupClauseExpr(List** flatresult, Bitmapset* seen_local,
     TargetEntry* tle = NULL;
     bool found = false;
 
+    if (DB_IS_CMPT(B_FORMAT) && gexpr && IsA(gexpr, UserSetElem)) {
+        pretransformAggWithUserSet(pstate, targetlist, gexpr, EXPR_KIND_GROUP_BY);
+        /* means nothing to deal in group by */
+        return 0;
+    }
+
     if (useSQL99) {
         tle = findTargetlistEntrySQL99(pstate, gexpr, targetlist, exprKind);
     } else {
@@ -2952,3 +2958,30 @@ static Node* transformFrameOffset(ParseState* pstate, int frameOptions, Node* cl
 
     return node;
 }
+
+/*
+ * special handle for UserSetElement used in group clause 
+ * it must set at top of targetList to get value before real 
+ * targetList to ensure @var appeard in real List got right
+ * value. resjunk must be true, because we do not want this
+ * UserSetElement actually appeared
+ */
+void pretransformAggWithUserSet(ParseState* pstate, List** targetList, Node* groupClause, ParseExprKind exprKind)
+{
+    ListCell* tllc = NULL;
+    TargetEntry* target = NULL;
+
+    Expr* expr = (Expr*)transformExpr(pstate, groupClause, exprKind);
+
+    TargetEntry* entry = makeTargetEntry((Expr*)expr, 1, NULL, true);
+
+    foreach (tllc, *targetList) {
+        target = (TargetEntry*)lfirst(tllc);
+        target->resno++; 
+    }
+    pstate->p_next_resno++;
+    *targetList = list_concat(list_make1(entry), *targetList);
+    pstate->p_target_list = *targetList;
+
+    return;
+}

src/include/parser/parse_clause.h

@@ -55,5 +55,6 @@ extern ParseNamespaceItem *makeNamespaceItem(RangeTblEntry *rte, bool lateral_on
  */
 extern void transformStartWith(ParseState *pstate, SelectStmt *stmt, Query *qry);
 extern void AddStartWithCTEPseudoReturnColumns(CommonTableExpr *cte, RangeTblEntry *rte, Index rte_index);
+extern void pretransformAggWithUserSet(ParseState* pstate, List** targetList, Node* groupClause, ParseExprKind exprKind);
 
 #endif /* PARSE_CLAUSE_H */

src/test/regress/expected/mysql_compatibility.out

@@ -1725,6 +1725,33 @@ INFO:  id+ is 4
  
 (1 row)
 
+--bugfix @var := expr in group by 
+drop table if exists tt_bug1 ;
+NOTICE:  table "tt_bug1" does not exist, skipping
+create  table tt_bug1(a int );
+insert into tt_bug1 values(1),(11),(111);
+SELECT a, @a, a as xx FROM tt_bug1 GROUP BY @a:= 999,a order by a ;
+  a  | @a  | xx  
+-----+-----+-----
+   1 | 999 |   1
+  11 | 999 |  11
+ 111 | 999 | 111
+(3 rows)
+
+SELECT a, @a, count(a) as xx FROM tt_bug1 GROUP BY @a:= a+11 ,a order by a ;
+  a  | @a  | xx 
+-----+-----+----
+   1 |  12 |  1
+  11 |  22 |  1
+ 111 | 122 |  1
+(3 rows)
+
+SELECT @a, avg(a) as xx FROM tt_bug1 GROUP BY @a:= 11;
+ @a |         xx          
+----+---------------------
+ 11 | 41.0000000000000000
+(1 row)
+
 set enable_set_variable_b_format = 0;
 select @var_t_1 := 2;
 ERROR:  syntax error at or near ":="

src/test/regress/sql/mysql_compatibility.sql

@@ -581,6 +581,16 @@ END;
 /
 call load_tbtest_WITH_REPLACE(3);
 
+
+--bugfix @var := expr in group by 
+drop table if exists tt_bug1 ;
+create  table tt_bug1(a int );
+insert into tt_bug1 values(1),(11),(111);
+SELECT a, @a, a as xx FROM tt_bug1 GROUP BY @a:= 999,a order by a ;
+SELECT a, @a, count(a) as xx FROM tt_bug1 GROUP BY @a:= a+11 ,a order by a ;
+SELECT @a, avg(a) as xx FROM tt_bug1 GROUP BY @a:= 11;
+
+
 set enable_set_variable_b_format = 0;
 select @var_t_1 := 2;