BUG#9998 MySQL client hangs on "USE database"

 Use open_normal_and_derived_tables instead of open_and_lock_tables when reading metadata for a table.
 Add two test cases, one for "USE database" and one for "SHOW COLUMNS FROM table"

mysql-test/r/lock_multi.result

@@ -36,3 +36,10 @@ lock table t1 write, t2 write;
 drop table t2;
 ERROR 42S02: Table 'test.t2' doesn't exist
 drop table t1;
+create table t1(a int);
+lock tables t1 write;
+show columns from t1;
+Field	Type	Null	Key	Default	Extra
+a	int(11)	YES		NULL	
+unlock tables;
+drop table t1;

mysql-test/r/mysql.result

@@ -48,3 +48,9 @@ Test  'go' command g
 a
 1
 drop table t1;
+create table t1(a int);
+lock tables t1 write;
+database()
+test
+unlock tables;
+drop table t1;

mysql-test/t/lock_multi.test

@@ -94,3 +94,15 @@ connection reader;
 reap;
 connection locker;
 drop table t1;
+
+
+#
+# BUG#9998 - MySQL client hangs on USE "database"
+
+create table t1(a int);
+lock tables t1 write;
+connection reader;
+show columns from t1;
+connection locker;
+unlock tables;
+drop table t1;

mysql-test/t/mysql.test

@@ -30,5 +30,14 @@ select "Test 'go' command(vertical output) \G" as " ";
 select "Test  'go' command \g" as " ";
 --exec $MYSQL test -e 'select * from t1\g'
 --enable_query_log
+drop table t1;
 
+#
+# BUG9998 - MySQL client hangs on USE "database"
+#
+create table t1(a int);
+lock tables t1 write;
+--exec $MYSQL -e 'use test; select database();'
+unlock tables;
 drop table t1;
+

sql/sql_show.cc

@@ -348,7 +348,7 @@ mysqld_show_create(THD *thd, TABLE_LIST *table_list)
                       table_list->table_name));
 
   /* Only one table for now, but VIEW can involve several tables */
-  if (open_and_lock_tables(thd, table_list))
+  if (open_normal_and_derived_tables(thd, table_list))
   {
     DBUG_RETURN(TRUE);
   }
@@ -539,8 +539,7 @@ mysqld_list_fields(THD *thd, TABLE_LIST *table_list, const char *wild)
   DBUG_ENTER("mysqld_list_fields");
   DBUG_PRINT("enter",("table: %s",table_list->table_name));
 
-  table_list->lock_type= TL_UNLOCK;
-  if (open_and_lock_tables(thd, table_list))
+  if (open_normal_and_derived_tables(thd, table_list))
     DBUG_VOID_RETURN;
   table= table_list->table;
 
@@ -1938,7 +1937,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
     bool res;
 
     lex->all_selects_list= lsel;
-    res= open_and_lock_tables(thd, show_table_list);
+    res= open_normal_and_derived_tables(thd, show_table_list);
     if (schema_table->process_table(thd, show_table_list,
                                     table, res, show_table_list->db,
                                     show_table_list->alias))
@@ -2043,7 +2042,7 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
             show_table_list->lock_type= lock_type;
             lex->all_selects_list= &sel;
             lex->derived_tables= 0;
-            res= open_and_lock_tables(thd, show_table_list);
+            res= open_normal_and_derived_tables(thd, show_table_list);
             if (schema_table->process_table(thd, show_table_list, table,
                                             res, base_name,
                                             show_table_list->alias))