Fixed bug #27937: crash for the the second execution of a prepared

statement from a UNION query with ORDER BY an expression containing
RAND().
The crash happened because the global order by list in the union query
was not re-initialized for execution.
(Local order by lists were re-initialized though).

mysql-test/r/ps.result

@@ -1087,4 +1087,26 @@ t2	CREATE TABLE `t2` (
 drop database mysqltest;
 deallocate prepare stmt1;
 deallocate prepare stmt2;
+CREATE TABLE t1(a int);
+INSERT INTO t1 VALUES (2), (3), (1);
+PREPARE st1 FROM
+'(SELECT a FROM t1) UNION (SELECT a+10 FROM t1) ORDER BY RAND()*0+a';
+EXECUTE st1;
+a
+1
+2
+3
+11
+12
+13
+EXECUTE st1;
+a
+1
+2
+3
+11
+12
+13
+DEALLOCATE PREPARE st1;
+DROP TABLE t1;
 End of 4.1 tests.

mysql-test/t/ps.test

@@ -1128,4 +1128,22 @@ drop database mysqltest;
 deallocate prepare stmt1;
 deallocate prepare stmt2;
 #
+
+#
+# Bug #27937: crash on the second execution for prepared statement 
+#             from UNION with ORDER BY an expression containing RAND()
+#
+
+CREATE TABLE t1(a int);
+INSERT INTO t1 VALUES (2), (3), (1);
+
+PREPARE st1 FROM
+  '(SELECT a FROM t1) UNION (SELECT a+10 FROM t1) ORDER BY RAND()*0+a';
+
+EXECUTE st1;
+EXECUTE st1;
+
+DEALLOCATE PREPARE st1;
+DROP TABLE t1;
+
 --echo End of 4.1 tests.

sql/sql_union.cc

@@ -135,6 +135,11 @@ st_select_lex_unit::init_prepare_fake_select_lex(THD *thd)
   fake_select_lex->table_list.link_in_list((byte *)&result_table_list,
 					   (byte **)
 					   &result_table_list.next);
+  for (ORDER *order= (ORDER *) global_parameters->order_list.first;
+       order;
+       order= order->next)
+    order->item= &order->item_ptr;
+
   return options_tmp;
 }