Fixed bug#18503: Queries with a quantified subquery returning empty set

may return a wrong result.

An Item_sum_hybrid object has the was_values flag which indicates whether any
values were added to the sum function. By default it is set to true and reset
to false on any no_rows_in_result() call. This method is called only in
return_zero_rows() function. An ALL/ANY subquery can be optimized by MIN/MAX
optimization. The was_values flag is used to indicate whether the subquery
has returned at least one row. This bug occurs because return_zero_rows() is
called only when we know that the select will return zero rows before
starting any scans but often such information is not known.
In the reported case the return_zero_rows() function is not called and
the was_values flag is not reset to false and yet the subquery return no rows
Item_func_not_all and Item_func_nop_all functions return a wrong
comparison result.

The end_send_group() function now calls no_rows_in_result() for each item
in the fields_list if there is no rows were found for the (sub)query.

mysql-test/r/subselect.result

@@ -2835,3 +2835,18 @@ a
 4
 DROP TABLE t1,t2,t3;
 purge master logs before (select adddate(current_timestamp(), interval -4 day));
+CREATE TABLE t1 (f1 INT);
+CREATE TABLE t2 (f2 INT);
+INSERT INTO t1 VALUES (1);
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2);
+f1
+1
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2 WHERE 1=0);
+f1
+1
+INSERT INTO t2 VALUES (1);
+INSERT INTO t2 VALUES (2);
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2 WHERE f2=0);
+f1
+1
+DROP TABLE t1, t2;

mysql-test/t/subselect.test

@@ -1820,4 +1820,18 @@ DROP TABLE t1,t2,t3;
 
 purge master logs before (select adddate(current_timestamp(), interval -4 day));
 
+
+#
+# Bug#18503: Queries with a quantified subquery returning empty set may
+# return a wrong result. 
+#
+CREATE TABLE t1 (f1 INT);
+CREATE TABLE t2 (f2 INT);
+INSERT INTO t1 VALUES (1);
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2);
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2 WHERE 1=0);
+INSERT INTO t2 VALUES (1);
+INSERT INTO t2 VALUES (2);
+SELECT * FROM t1 WHERE f1 > ALL (SELECT f2 FROM t2 WHERE f2=0);
+DROP TABLE t1, t2;
 # End of 4.1 tests

sql/sql_select.cc

@@ -6746,8 +6746,13 @@ end_send_group(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
 	{
 	  if (!join->first_record)
 	  {
+            List_iterator_fast<Item> it(*join->fields);
+            Item *item;
 	    /* No matching rows for group function */
 	    join->clear();
+
+            while ((item= it++))
+              item->no_rows_in_result();
 	  }
 	  if (join->having && join->having->val_int() == 0)
 	    error= -1;				// Didn't satisfy having