Bug#23588 SHOW COLUMNS on a temporary table causes locking issues

skip lock_type update for temporary tables

mysql-test/r/tablelock.result

@@ -46,3 +46,12 @@ CREATE TABLE t2 (a int);
 lock tables t1 write,t1 as b write, t2 write, t2 as c read;
 drop table t2,t1;
 unlock tables;
+create temporary table t1(f1 int);
+lock tables t1 write;
+insert into t1 values (1);
+show columns from t1;
+Field	Type	Null	Key	Default	Extra
+f1	int(11)	YES		NULL	
+insert into t1 values(2);
+drop table t1;
+unlock tables;

mysql-test/t/tablelock.test

@@ -49,3 +49,16 @@ drop table t2,t1;
 unlock tables;
 
 # End of 4.1 tests
+
+#
+# Bug#23588 SHOW COLUMNS on a temporary table causes locking issues
+#
+create temporary table t1(f1 int);
+lock tables t1 write;
+insert into t1 values (1);
+show columns from t1;
+insert into t1 values(2);
+drop table t1;
+unlock tables;
+
+# End of 5.0 tests

sql/sql_base.cc

@@ -2852,8 +2852,12 @@ int open_tables(THD *thd, TABLE_LIST **start, uint *counter, uint flags)
     }
 
     if (tables->lock_type != TL_UNLOCK && ! thd->locked_tables)
-      tables->table->reginfo.lock_type= tables->lock_type == TL_WRITE_DEFAULT ?
-        thd->update_lock_default : tables->lock_type;
+    {
+      if (tables->lock_type == TL_WRITE_DEFAULT)
+        tables->table->reginfo.lock_type= thd->update_lock_default;
+      else if (tables->table->s->tmp_table == NO_TMP_TABLE)
+        tables->table->reginfo.lock_type= tables->lock_type;
+    }
     tables->table->grant= tables->grant;
 
 process_view_routines: