MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions

We need to ensure that all the unions are marked as UNCACHEABLE_RAND in
cases like:
  select * from t1 where 1 in (select 1 union select 2 union select RAND());

Author: DaveGosselin-MariaDB

mysql-test/main/subselect.result

@@ -7642,3 +7642,13 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests

mysql-test/main/subselect.test

@@ -6501,3 +6501,13 @@ DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 
 --echo # End of 10.10 tests
+
+--echo #
+--echo # MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+--echo #
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+drop table t1;
+
+--echo # End of 12.2 tests

mysql-test/main/subselect_no_exists_to_in.result

@@ -7644,6 +7644,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%exists_to_in=off%';
 @@optimizer_switch like '%exists_to_in=off%'

mysql-test/main/subselect_no_mat.result

@@ -7639,6 +7639,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%materialization=on%';
 @@optimizer_switch like '%materialization=on%'

mysql-test/main/subselect_no_opts.result

@@ -7637,4 +7637,14 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set @optimizer_switch_for_subselect_test=null;

mysql-test/main/subselect_no_scache.result

@@ -7648,6 +7648,16 @@ Warning	1292	Truncated incorrect DECIMAL value: 'e'
 DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
+#
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
 set optimizer_switch=default;
 select @@optimizer_switch like '%subquery_cache=on%';
 @@optimizer_switch like '%subquery_cache=on%'

mysql-test/main/subselect_no_semijoin.result

@@ -7638,6 +7638,16 @@ DROP VIEW v1;
 DROP TABLE t1, t2, t3;
 # End of 10.10 tests
 #
+# MDEV-37905: UNCACHEABLE_RAND inconsistently set on unions
+#
+create table t1 (a int);
+insert into t1 (a) values (1);
+select * from t1 where 1 in (select 1 union select 2 union select RAND());
+a
+1
+drop table t1;
+# End of 12.2 tests
+#
 # MDEV-19714: JOIN::pseudo_bits_cond is not visible in EXPLAIN FORMAT=JSON
 #
 CREATE TABLE t1 ( a INT );

sql/sql_lex.cc

@@ -5131,6 +5131,19 @@ bool st_select_lex::optimize_unflattened_subqueries(bool const_only)
       else
         un->uncacheable&= ~UNCACHEABLE_DEPENDENT;
       subquery_predicate->is_correlated= is_correlated_unit;
+
+#ifdef DBUG_ASSERT_EXISTS
+      /*
+        If any SELECT in the unit is marked as UNCACHEABLE_RAND, then the
+        unit itself should also be marked as UNCACHEABLE_RAND.
+      */
+      bool has_rand= false;
+      for (SELECT_LEX *sl= un->first_select(); sl && !has_rand;
+           sl= sl->next_select())
+        has_rand= sl->uncacheable & UNCACHEABLE_RAND;
+      DBUG_ASSERT(has_rand ==
+                  static_cast<bool>(un->uncacheable & UNCACHEABLE_RAND));
+#endif
     }
   }
   return FALSE;
@@ -11351,6 +11364,7 @@ SELECT_LEX_UNIT *LEX::parsed_select_expr_cont(SELECT_LEX_UNIT *unit,
   }
   last->link_neighbour(sel1);
   sel1->set_master_unit(unit);
+  unit->uncacheable |= sel1->uncacheable;
   sel1->set_linkage_and_distinct(unit_type, distinct);
   unit->pre_last_parse= last;
   return unit;