Bug #32036: EXISTS within a WHERE clause with a UNION

  crashes MySQL 5.122
There was a difference in how UNIONs are handled
on top level and when in sub-query.
Because the rules for sub-queries were syntactically
allowing cases that are not currently supported by
the server we had crashes (this bug) or wrong results
(bug 32051).
Fixed by making the syntax rules for UNIONs match the 
ones at top level.

These rules however do not support nesting UNIONs, e.g.
(SELECT a FROM t1 UNION ALL SELECT b FROM t2) 
 UNION
(SELECT c FROM t3 UNION ALL SELECT d FROM t4)
Supports for statements with nested UNIONs will be
added in a future version.


mysql-test/r/subselect.result:
  Bug #32036: test case
mysql-test/t/subselect.test:
  Bug #32036: test case
sql/sql_yacc.yy:
  Bug #32036: Make the syntax rules for UNIONs in subqueries the same
  as for top level UNIONs.

1 files changed, 14 insertions, 27 deletions

diff --git a/sql/sql_yacc.yy b/sql/sql_yacc.yy
index 3401bf739b3..2e2a9b180d0 100644
--- a/sql/sql_yacc.yy
+++ b/sql/sql_yacc.yy
@@ -1137,7 +1137,7 @@ bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 
 %type <variable> internal_variable_name
 
-%type <select_lex> subselect subselect_init
+%type <select_lex> subselect take_first_select
 	get_select_lex
 
 %type <boolfunc2creator> comp_op
@@ -9422,35 +9422,22 @@ union_option:
 	| ALL       { $$=0; }
         ;
 
+take_first_select: /* empty */
+        {
+          $$= Lex->current_select->master_unit()->first_select();
+        };
+
 subselect:
-        SELECT_SYM subselect_start subselect_init subselect_end
+        SELECT_SYM subselect_start select_init2 take_first_select 
+        subselect_end
         {
-          $$= $3;
+          $$= $4;
         }
-        | '(' subselect_start subselect ')'
-          {
-	    THD *thd= YYTHD;
-            /*
-              note that a local variable can't be used for
-              $3 as it's used in local variable construction
-              and some compilers can't guarnatee the order
-              in which the local variables are initialized.
-            */
-            List_iterator<Item> it($3->item_list);
-            Item *item;
-            /*
-              we must fill the items list for the "derived table".
-            */
-            while ((item= it++))
-              add_item_to_list(thd, item);
-          }
-          union_clause subselect_end { $$= $3; };
-
-subselect_init:
-  select_init2
-  {
-    $$= Lex->current_select->master_unit()->first_select();
-  };
+        | '(' subselect_start select_paren take_first_select 
+        subselect_end ')'
+        {
+          $$= $4;
+        };
 
 subselect_start:
 	{