Fixed bug #25219: crash for a query that contains an EXIST subquery with

UNION over correlated and uncorrelated SELECTS.
In such subqueries each uncorrelated SELECT should be considered as
uncacheable. Otherwise join_free is called for it and in many cases
it causes some problems.

mysql-test/r/subselect.result

@@ -3605,3 +3605,36 @@ FROM t1) t;
 COUNT(*)
 3000
 DROP TABLE t1,t2;
+CREATE TABLE t1 (id char(4) PRIMARY KEY, c int);
+CREATE TABLE t2 (c int);
+INSERT INTO t1 VALUES ('aa', 1);
+INSERT INTO t2 VALUES (1);
+SELECT * FROM t1 
+WHERE EXISTS (SELECT c FROM t2 WHERE c=1
+UNION 
+SELECT c from t2 WHERE c=t1.c);
+id	c
+aa	1
+INSERT INTO t1 VALUES ('bb', 2), ('cc', 3), ('dd',1);
+SELECT * FROM t1 
+WHERE EXISTS (SELECT c FROM t2 WHERE c=1
+UNION 
+SELECT c from t2 WHERE c=t1.c);
+id	c
+aa	1
+bb	2
+cc	3
+dd	1
+INSERT INTO t2 VALUES (2);
+CREATE TABLE t3 (c int);
+INSERT INTO t3 VALUES (1);
+SELECT * FROM t1 
+WHERE EXISTS (SELECT t2.c FROM t2 JOIN t3 ON t2.c=t3.c WHERE t2.c=1
+UNION 
+SELECT c from t2 WHERE c=t1.c);
+id	c
+aa	1
+bb	2
+cc	3
+dd	1
+DROP TABLE t1,t2,t3;

mysql-test/t/subselect.test

@@ -2508,3 +2508,37 @@ SELECT SQL_NO_CACHE COUNT(*)
           FROM t1) t;
 
 DROP TABLE t1,t2;
+
+#
+# Bug #25219: EXIST subquery with UNION over a mix of
+#             correlated and uncorrelated selects
+#             
+
+CREATE TABLE t1 (id char(4) PRIMARY KEY, c int);
+CREATE TABLE t2 (c int);
+
+INSERT INTO t1 VALUES ('aa', 1);
+INSERT INTO t2 VALUES (1);
+
+SELECT * FROM t1 
+  WHERE EXISTS (SELECT c FROM t2 WHERE c=1
+                UNION 
+                SELECT c from t2 WHERE c=t1.c);
+
+INSERT INTO t1 VALUES ('bb', 2), ('cc', 3), ('dd',1);
+
+SELECT * FROM t1 
+  WHERE EXISTS (SELECT c FROM t2 WHERE c=1
+                UNION 
+                SELECT c from t2 WHERE c=t1.c);
+
+INSERT INTO t2 VALUES (2);
+CREATE TABLE t3 (c int);
+INSERT INTO t3 VALUES (1);
+
+SELECT * FROM t1 
+  WHERE EXISTS (SELECT t2.c FROM t2 JOIN t3 ON t2.c=t3.c WHERE t2.c=1
+                UNION 
+                SELECT c from t2 WHERE c=t1.c);
+
+DROP TABLE t1,t2,t3;

sql/mysql_priv.h

@@ -410,7 +410,10 @@ MY_LOCALE *my_locale_by_name(const char *name);
 #define UNCACHEABLE_EXPLAIN     8
 /* Don't evaluate subqueries in prepare even if they're not correlated */
 #define UNCACHEABLE_PREPARE    16
-/* Used to chack GROUP BY list in the MODE_ONLY_FULL_GROUP_BY mode */
+/* For uncorrelated SELECT in an UNION with some correlated SELECTs */
+#define UNCACHEABLE_UNITED     32
+
+/* Used to check GROUP BY list in the MODE_ONLY_FULL_GROUP_BY mode */
 #define UNDEF_POS (-1)
 #ifdef EXTRA_DEBUG
 /*

sql/sql_lex.cc

@@ -1371,9 +1371,17 @@ void st_select_lex::mark_as_dependent(SELECT_LEX *last)
     if (!(s->uncacheable & UNCACHEABLE_DEPENDENT))
     {
       // Select is dependent of outer select
-      s->uncacheable|= UNCACHEABLE_DEPENDENT;
+      s->uncacheable= (s->uncacheable & ~UNCACHEABLE_UNITED) |
+                       UNCACHEABLE_DEPENDENT;
       SELECT_LEX_UNIT *munit= s->master_unit();
-      munit->uncacheable|= UNCACHEABLE_DEPENDENT;
+      munit->uncacheable= (munit->uncacheable & ~UNCACHEABLE_UNITED) |
+                       UNCACHEABLE_DEPENDENT;
+      for (SELECT_LEX *sl= munit->first_select(); sl ; sl= sl->next_select())
+      {
+        if (sl != s &&
+            !(sl->uncacheable & (UNCACHEABLE_DEPENDENT | UNCACHEABLE_UNITED)))
+          sl->uncacheable|= UNCACHEABLE_UNITED;
+      }
     }
   is_correlated= TRUE;
   this->master_unit()->item->is_correlated= TRUE;