Merge stella.local:/home2/mydev/mysql-5.0-axmrg

into  stella.local:/home2/mydev/mysql-5.1-axmrg

mysql-test/r/merge.result

@@ -964,6 +964,28 @@ id	ref
 3	2
 4	5
 DROP TABLE t1, t2, t3;
+CREATE TABLE t1(a INT);
+CREATE TABLE m1(a INT) ENGINE=MERGE;
+SHOW CREATE TABLE m1;
+Table	Create Table
+m1	CREATE TABLE `m1` (
+  `a` int(11) default NULL
+) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1
+DROP TABLE m1;
+CREATE TABLE m1(a INT) ENGINE=MERGE UNION=();
+SHOW CREATE TABLE m1;
+Table	Create Table
+m1	CREATE TABLE `m1` (
+  `a` int(11) default NULL
+) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1
+ALTER TABLE m1 UNION=(t1);
+ALTER TABLE m1 UNION=();
+SHOW CREATE TABLE m1;
+Table	Create Table
+m1	CREATE TABLE `m1` (
+  `a` int(11) default NULL
+) ENGINE=MRG_MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1, m1;
 End of 5.0 tests
 create table t1 (c1 int, index(c1));
 create table t2 (c1 int, index(c1)) engine=merge union=(t1);

mysql-test/t/merge.test

@@ -599,6 +599,19 @@ SELECT * FROM t3;
 
 DROP TABLE t1, t2, t3;
 
+#
+# BUG#28248 - mysqldump results with MERGE ... UNION=() cannot be executed
+#
+CREATE TABLE t1(a INT);
+CREATE TABLE m1(a INT) ENGINE=MERGE;
+SHOW CREATE TABLE m1;
+DROP TABLE m1;
+CREATE TABLE m1(a INT) ENGINE=MERGE UNION=();
+SHOW CREATE TABLE m1;
+ALTER TABLE m1 UNION=(t1);
+ALTER TABLE m1 UNION=();
+SHOW CREATE TABLE m1;
+DROP TABLE t1, m1;
 
 --echo End of 5.0 tests
 

sql/sql_yacc.yy

@@ -4357,7 +4357,7 @@ create_table_option:
             Lex->create_info.row_type= $3;
             Lex->create_info.used_fields|= HA_CREATE_USED_ROW_FORMAT;
           }
-        | UNION_SYM opt_equal '(' table_list ')'
+        | UNION_SYM opt_equal '(' opt_table_list ')'
           {
             /* Move the union list to the merge_list */
             LEX *lex=Lex;

storage/myisammrg/ha_myisammrg.cc

@@ -1102,6 +1102,12 @@ void ha_myisammrg::append_create_info(String *packet)
     packet->append(STRING_WITH_LEN(" INSERT_METHOD="));
     packet->append(get_type(&merge_insert_method,file->merge_insert_method-1));
   }
+  /*
+    There is no sence adding UNION clause in case there is no underlying
+    tables specified.
+  */
+  if (file->open_tables == file->end_table)
+    return;
   packet->append(STRING_WITH_LEN(" UNION=("));
 
   current_db= table->s->db.str;