Fixed LP bug #791761.

An aggregating query over an empty set of a join of two tables
with a rejecting HAVING clause erroneously could return a row.
It could happen in the cases when the optimizer made a conclusion
that the aggregating set was empty.
Wrong results were produced because the server missed initial
setting for aggregation functions in the mentioned cases.
      

mysql-test/r/having.result

@@ -570,3 +570,27 @@ ORDER BY t1.f1;
 f1
 DROP TABLE t1,t2;
 End of 5.1 tests
+#
+# LP bug #791761: MAX over an empty join + HAVING
+#
+CREATE TABLE t1 (a int, b int , KEY (b)) ;
+INSERT INTO t1 VALUES (3,1);
+CREATE TABLE t2 (a int NOT NULL ) ;
+INSERT INTO t2 VALUES (29);
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a > 0 HAVING MAX(t1.b) <> 6;
+MAX(t1.b)
+1
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a > 0 HAVING MAX(t1.b) IS NULL;
+MAX(t1.b)
+EXPLAIN
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a < 0 HAVING MAX(t1.b) <> 6;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a < 0 HAVING MAX(t1.b) <> 6;
+MAX(t1.b)
+CREATE TABLE t3 ( f3 int) ;
+INSERT INTO t3 VALUES (NULL);
+SELECT MAX(t1.b) AS f FROM t1 JOIN t2 ON t2.a != 0
+WHERE (SELECT f3 FROM t3) <> 0 HAVING f <> 6 ;
+f
+DROP TABLE t1,t2,t3;

mysql-test/t/having.test

@@ -591,3 +591,28 @@ DROP TABLE t1,t2;
 
 
 --echo End of 5.1 tests
+
+--echo #
+--echo # LP bug #791761: MAX over an empty join + HAVING
+--echo #
+
+CREATE TABLE t1 (a int, b int , KEY (b)) ;
+INSERT INTO t1 VALUES (3,1);
+
+CREATE TABLE t2 (a int NOT NULL ) ;
+INSERT INTO t2 VALUES (29);
+
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a > 0 HAVING MAX(t1.b) <> 6;
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a > 0 HAVING MAX(t1.b) IS NULL;
+
+EXPLAIN
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a < 0 HAVING MAX(t1.b) <> 6;
+SELECT MAX(t1.b)  FROM t1,t2 WHERE t2.a < 0 HAVING MAX(t1.b) <> 6;
+
+CREATE TABLE t3 ( f3 int) ;
+INSERT INTO t3 VALUES (NULL);
+
+SELECT MAX(t1.b) AS f FROM t1 JOIN t2 ON t2.a != 0
+  WHERE (SELECT f3 FROM t3) <> 0 HAVING f <> 6 ;
+
+DROP TABLE t1,t2,t3;

sql/item.h

@@ -1020,6 +1020,7 @@ class Item {
   virtual bool set_fake_select_as_master_processor(uchar *arg) { return 0; }
   virtual bool view_used_tables_processor(uchar *arg) { return 0; }
   virtual bool eval_not_null_tables(uchar *opt_arg) { return 0; }
+  virtual bool clear_sum_processor(uchar *opt_arg) { return 0; }
 
   /* To call bool function for all arguments */
   struct bool_func_call_args

sql/item_sum.h

@@ -388,6 +388,7 @@ class Item_sum :public Item_result_field
   {
     return trace_unsupported_by_check_vcol_func_processor(func_name()); 
   }
+  bool clear_sum_processor(uchar *arg) { clear(); return 0; }
 };
 
 

sql/sql_select.cc

@@ -10146,7 +10146,9 @@ return_zero_rows(JOIN *join, select_result *result, List<TABLE_LIST> &tables,
     TABLE_LIST *table;
     while ((table= ti++))
       mark_as_null_row(table->table);		// All fields are NULL
-    if (having && having->val_int() == 0)
+    if (having &&
+        !having->walk(&Item::clear_sum_processor, FALSE, NULL) &&
+        having->val_int() == 0)
       send_row=0;
   }
   if (!(result->send_fields(fields,