Test that all MERGE tables comes from the same database

Docs/manual.texi:
  Changelog and more documentation about ALTER TABLE
include/mysqld_error.h:
  New error message
mysql-test/t/merge.test:
  Test of error conditions
sql/gen_lex_hash.cc:
  Smaller array
sql/ha_myisammrg.cc:
  Cleanup
sql/share/czech/errmsg.txt:
  New message
sql/share/danish/errmsg.txt:
  New message
sql/share/dutch/errmsg.txt:
  New message
sql/share/english/errmsg.txt:
  New message
sql/share/estonian/errmsg.txt:
  New message
sql/share/french/errmsg.txt:
  New message
sql/share/german/errmsg.txt:
  New message
sql/share/greek/errmsg.txt:
  New message
sql/share/hungarian/errmsg.txt:
  New message
sql/share/italian/errmsg.txt:
  New message
sql/share/japanese/errmsg.txt:
  New message
sql/share/korean/errmsg.txt:
  New message
sql/share/norwegian-ny/errmsg.txt:
  New message
sql/share/norwegian/errmsg.txt:
  New message
sql/share/polish/errmsg.txt:
  New message
sql/share/portuguese/errmsg.txt:
  New message
sql/share/romanian/errmsg.txt:
  New message
sql/share/russian/errmsg.txt:
  New message
sql/share/slovak/errmsg.txt:
  New message
sql/share/spanish/errmsg.txt:
  New message
sql/share/swedish/errmsg.txt:
  New message

1 files changed, 10 insertions, 2 deletions

diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 2e5333925e7..99fc0fc8fbf 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -2178,10 +2178,18 @@ static bool check_merge_table_access(THD *thd, char *db,
   int error=0;
   if (table_list)
   {
-    /* Force all tables to use the current database */
+    /* Check that all tables use the current database */
     TABLE_LIST *tmp;
     for (tmp=table_list; tmp ; tmp=tmp->next)
-      tmp->db=db;
+    {
+      if (!tmp->db || !tmp->db[0])
+	tmp->db=db;
+      else if (!strcmp(tmp->db,db))
+      {
+	send_error(&thd->net,ER_UNION_TABLES_IN_DIFFERENT_DIR);
+	return 1;
+      }
+    }
     error=check_table_access(thd, SELECT_ACL | UPDATE_ACL | DELETE_ACL,
 			     table_list);
   }