Bug#38499: flush tables and multitable table update with

           derived table cause crash

When a multi-UPDATE command fails to lock some table, and
subsequently succeeds, the tables need to be reopened if
they were altered. But the reopening procedure failed for
derived tables.

Extra cleanup has been added.


mysql-test/r/lock_multi.result:
  Added test case for bug #38499.
mysql-test/t/lock_multi.test:
  Added test case for bug #38499.
sql/sql_union.cc:
  Bug#38499: flush tables and multitable table update with
             derived table cause crash
  
  Obsolete assertion has been removed.
sql/sql_update.cc:
  Bug#38499: flush tables and multitable table update with
             derived table cause crash
  
  Extra cleanup for derived tables has been added:
  1) unit.cleanup(),
  2) unit->reinit_exec_mechanism().

mysql-test/r/lock_multi.result

@@ -115,3 +115,21 @@ CREATE TABLE t3 SELECT * FROM t1;
 # normal mode
 # PS mode
 DROP TABLE t1, t2, t3;
+CREATE TABLE t1( a INT, b INT );
+INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (4, 4);
+# 1. test regular tables
+# 1.1. test altering of columns that multiupdate doesn't use
+# 1.1.1. normal mode
+# 1.1.2. PS mode
+# 1.2. test altering of columns that multiupdate uses
+# 1.2.1. normal mode
+# 1.2.2. PS mode
+ALTER TABLE t1 ADD COLUMN a INT;
+# 2. test UNIONs
+# 2.1. test altering of columns that multiupdate doesn't use
+# 2.1.1. normal mode
+# 2.1.2. PS mode
+# 2.2. test altering of columns that multiupdate uses
+# 2.2.1. normal mode
+# 2.2.2. PS mode
+DROP TABLE t1;

mysql-test/t/lock_multi.test

@@ -400,4 +400,206 @@ while ($i) {
 --connection default
 DROP TABLE t1, t2, t3;
 
+#
+# Bug#38499: flush tables and multitable table update with derived table cause 
+#            crash
+#
+
+CREATE TABLE t1( a INT, b INT );
+INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (4, 4);
+
+--echo # 1. test regular tables
+--echo # 1.1. test altering of columns that multiupdate doesn't use
+--echo # 1.1.1. normal mode
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+--dec $i
+
+--connection writer
+  send UPDATE t1, (SELECT 1 FROM t1 t1i) d SET a = 0 WHERE 1=0;
+
+--connection locker
+  ALTER TABLE t1 ADD COLUMN (c INT);
+  ALTER TABLE t1 DROP COLUMN c;
+
+--connection writer
+--reap
+}
+
+--echo # 1.1.2. PS mode
+
+--connection writer
+PREPARE stmt FROM 'UPDATE t1, (SELECT 1 FROM t1 t1i) d SET a = 0 WHERE 1=0';
+
+let $i = 100;
+while ($i) {
+--dec $i
+
+--connection writer
+--send EXECUTE stmt
+
+--connection locker
+  ALTER TABLE t1 ADD COLUMN (c INT);
+  ALTER TABLE t1 DROP COLUMN c;
+
+--connection writer
+--reap
+}
+--enable_query_log
+
+--echo # 1.2. test altering of columns that multiupdate uses
+--echo # 1.2.1. normal mode
+
+--connection default
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+  dec $i;
+
+--connection locker
+--error 0,1060
+  ALTER TABLE t1 ADD COLUMN a int(11) unsigned default NULL;
+  UPDATE t1 SET a=b;
+
+--connection writer
+--send UPDATE t1, (SELECT 1 FROM t1 t1i) d SET a = 0 WHERE 1=0;
+
+--connection locker
+--error 0,1091
+  ALTER TABLE t1 DROP COLUMN a;
+
+--connection writer
+--error 0,1054 # unknown column error
+--reap
+}
+--enable_query_log
+
+--echo # 1.2.2. PS mode
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+  dec $i;
+
+--connection locker
+--error 0,1060
+  ALTER TABLE t1 ADD COLUMN a INT;
+  UPDATE t1 SET a=b;
+
+--connection writer
+  PREPARE stmt FROM 'UPDATE t1, (SELECT 1 FROM t1 t1i) d SET a = 0 WHERE 1=0';
+--send EXECUTE stmt
+
+--connection locker
+--error 0,1091
+  ALTER TABLE t1 DROP COLUMN a;
+
+--connection writer
+--error 0,1054 # Unknown column 'a' in 'field list'
+--reap
+}
+--enable_query_log
+--connection default
+ALTER TABLE t1 ADD COLUMN a INT;
+
+--echo # 2. test UNIONs
+--echo # 2.1. test altering of columns that multiupdate doesn't use
+--echo # 2.1.1. normal mode
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+--dec $i
+
+--connection writer
+  send UPDATE t1, ((SELECT 1 FROM t1 t1i) UNION (SELECT 2 FROM t1 t1ii)) e SET a = 0 WHERE 1=0;
+
+--connection locker
+  ALTER TABLE t1 ADD COLUMN (c INT);
+  ALTER TABLE t1 DROP COLUMN c;
+
+--connection writer
+--reap
+}
+
+--echo # 2.1.2. PS mode
+
+--connection writer
+PREPARE stmt FROM 'UPDATE t1, ((SELECT 1 FROM t1 t1i) UNION (SELECT 2 FROM t1 t1ii)) e SET a = 0 WHERE 1=0';
+
+let $i = 100;
+while ($i) {
+--dec $i
+
+--connection writer
+--send EXECUTE stmt
+
+--connection locker
+  ALTER TABLE t1 ADD COLUMN (c INT);
+  ALTER TABLE t1 DROP COLUMN c;
+
+--connection writer
+--reap
+}
+--enable_query_log
+
+--echo # 2.2. test altering of columns that multiupdate uses
+--echo # 2.2.1. normal mode
+
+--connection default
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+  dec $i;
+
+--connection locker
+--error 0,1060
+  ALTER TABLE t1 ADD COLUMN a int(11) unsigned default NULL;
+  UPDATE t1 SET a=b;
+
+--connection writer
+--send UPDATE t1, ((SELECT 1 FROM t1 t1i) UNION (SELECT 2 FROM t1 t1ii)) e SET a = 0 WHERE 1=0;
+
+--connection locker
+--error 0,1091
+  ALTER TABLE t1 DROP COLUMN a;
+
+--connection writer
+--error 0,1054 # Unknown column 'a' in 'field list'
+--reap
+}
+--enable_query_log
+
+--echo # 2.2.2. PS mode
+
+--disable_query_log
+let $i = 100;
+while ($i) {
+  dec $i;
+
+--connection locker
+--error 0,1060
+  ALTER TABLE t1 ADD COLUMN a INT;
+  UPDATE t1 SET a=b;
+
+--connection writer
+  PREPARE stmt FROM 'UPDATE t1, ((SELECT 1 FROM t1 t1i) UNION (SELECT 2 FROM t1 t1ii)) e SET a = 0 WHERE 1=0';
+--send EXECUTE stmt
+
+--connection locker
+--error 0,1091
+  ALTER TABLE t1 DROP COLUMN a;
+
+--connection writer
+--error 0,1054 # Unknown column 'a' in 'field list'
+--reap
+}
+--enable_query_log
+--connection default
+DROP TABLE t1;
+
 # End of 5.0 tests

sql/sql_union.cc

@@ -399,7 +399,6 @@ bool st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result,
     }
     else
     {
-      DBUG_ASSERT(!thd->stmt_arena->is_conventional());
       /*
         We're in execution of a prepared statement or stored procedure:
         reset field items to point at fields from the created temporary table.

sql/sql_update.cc

@@ -875,6 +875,26 @@ int mysql_multi_update_prepare(THD *thd)
     for (TABLE_LIST *tbl= table_list; tbl; tbl= tbl->next_global)
       tbl->cleanup_items();
 
+    /*
+      To not to hog memory (as a result of the 
+      unit->reinit_exec_mechanism() call below):
+    */
+    lex->unit.cleanup();
+
+    for (SELECT_LEX *sl= lex->all_selects_list;
+        sl;
+        sl= sl->next_select_in_list())
+    {
+      SELECT_LEX_UNIT *unit= sl->master_unit();
+      unit->reinit_exec_mechanism(); // reset unit->prepared flags
+      /*
+        Reset 'clean' flag back to force normal execution of
+        unit->cleanup() in Prepared_statement::cleanup_stmt()
+        (call to lex->unit.cleanup() above sets this flag to TRUE).
+      */
+      unit->unclean();
+    }
+
     /*
       Also we need to cleanup Natural_join_column::table_field items.
       To not to traverse a join tree we will cleanup whole