Bug #31156: mysqld: item_sum.cc:918: virtual bool

  Item_sum_distinct::setup(THD*): Assertion

There was an assertion to detect a bug in ROLLUP
implementation. However the assertion is not true
when used in a subquery context with non-cacheable
statements.
Fixed by turning the assertion to accepted case
(just like it's done for the other aggregate functions). 

mysql-test/r/func_group.result

@@ -1377,4 +1377,14 @@ SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1 and b > 1;
 MIN(a)	MIN(b)
 1	2
 DROP TABLE t1, t2, t3, t4, t5;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 values (),(),();
+SELECT (SELECT SLEEP(0) FROM t1 ORDER BY AVG(DISTINCT a) ) as x FROM t1 
+GROUP BY x;
+x
+0
+SELECT 1 FROM t1 GROUP BY (SELECT SLEEP(0) FROM t1 ORDER BY AVG(DISTINCT a) );
+1
+1
+DROP TABLE t1;
 End of 5.0 tests

mysql-test/t/func_group.test

@@ -860,5 +860,18 @@ SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1 and b > 1;
 
 DROP TABLE t1, t2, t3, t4, t5;
 
+#
+# Bug #31156: mysqld: item_sum.cc:918: 
+#  virtual bool Item_sum_distinct::setup(THD*): Assertion
+#
+
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 values (),(),();
+SELECT (SELECT SLEEP(0) FROM t1 ORDER BY AVG(DISTINCT a) ) as x FROM t1 
+  GROUP BY x;
+SELECT 1 FROM t1 GROUP BY (SELECT SLEEP(0) FROM t1 ORDER BY AVG(DISTINCT a) );
+
+DROP TABLE t1;
+
 ###
 --echo End of 5.0 tests

sql/item_sum.cc

@@ -905,7 +905,9 @@ bool Item_sum_distinct::setup(THD *thd)
   List<create_field> field_list;
   create_field field_def;                              /* field definition */
   DBUG_ENTER("Item_sum_distinct::setup");
-  DBUG_ASSERT(tree == 0);
+  /* It's legal to call setup() more than once when in a subquery */
+  if (tree)
+    return FALSE;
 
   /*
     Virtual table and the tree are created anew on each re-execution of
@@ -2443,6 +2445,7 @@ bool Item_sum_count_distinct::setup(THD *thd)
   /*
     Setup can be called twice for ROLLUP items. This is a bug.
     Please add DBUG_ASSERT(tree == 0) here when it's fixed.
+    It's legal to call setup() more than once when in a subquery
   */
   if (tree || table || tmp_table_param)
     return FALSE;