Bug #47919 assert in open_table during ALTER temporary table

This assertion would occur if UPDATE was used to update multiple
tables containing an AUTO_INCREMENT column and if the inserted
row had a user-supplied value for that column. The assertion 
could then be triggered by the next statement.

The problem was only noticeable on debug builds of the server.

The cause of the problem was that the code for multi update did
not properly reset the TABLE->auto_increment_if_null flag after update.
The flag is used to indicate that a non-null value of an auto_increment field
has been provided by the user or retrieved from a current record.
Open_tables() contains an assertion that tests this flag, and this
was triggered in this case by ALTER TABLE.

This patch fixes the problem by resetting the auto_increment_if_null
field to FALSE once a row has been updated.

This bug is similar to Bug#47274, but for multi update rather
than INSERT DELAYED.

Test case added to update.test.

mysql-test/r/update.result

@@ -503,3 +503,14 @@ ERROR HY000: Recursive stored functions and triggers are not allowed.
 DROP TABLE t1;
 DROP FUNCTION f1;
 End of 5.0 tests
+#
+# Bug #47919 assert in open_table during ALTER temporary table
+#
+CREATE TABLE t1 (f1 INTEGER AUTO_INCREMENT, PRIMARY KEY (f1));
+CREATE TEMPORARY TABLE t2 LIKE t1;
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+ALTER TABLE t2 COMMENT = 'ABC';
+UPDATE t2, t1 SET t2.f1 = 2, t1.f1 = 9;
+ALTER TABLE t2 COMMENT = 'DEF';
+DROP TABLE t1, t2;

mysql-test/t/update.test

@@ -452,3 +452,18 @@ DROP TABLE t1;
 DROP FUNCTION f1;
 
 --echo End of 5.0 tests
+
+--echo #
+--echo # Bug #47919 assert in open_table during ALTER temporary table
+--echo #
+
+CREATE TABLE t1 (f1 INTEGER AUTO_INCREMENT, PRIMARY KEY (f1));
+CREATE TEMPORARY TABLE t2 LIKE t1;
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+
+ALTER TABLE t2 COMMENT = 'ABC';
+UPDATE t2, t1 SET t2.f1 = 2, t1.f1 = 9;
+ALTER TABLE t2 COMMENT = 'DEF';
+
+DROP TABLE t1, t2;

sql/sql_update.cc

@@ -1696,6 +1696,11 @@ bool multi_update::send_data(List<Item> &not_used_values)
                                                TRG_EVENT_UPDATE))
 	DBUG_RETURN(1);
 
+      /*
+        Reset the table->auto_increment_field_not_null as it is valid for
+        only one row.
+      */
+      table->auto_increment_field_not_null= FALSE;
       found++;
       if (!can_compare_record || compare_record(table))
       {