Fix for BUG#8023.

Allow LIMIT clause after DUAL.


mysql-test/r/limit.result:
  Added test result for BUG#8023.
mysql-test/t/limit.test:
  Added test for BUG#8023.
sql/sql_yacc.yy:
  Allow the specification of a LIMIT clause after DUAL. This is needed for queries as:
  select a from t1 union all select 1 from dual limit 1;
  In this query LIMIT is applied to the whole UNION, so it makes sense, however, the
  current parser did not allow any clause after DUAL.

mysql-test/r/limit.result

@@ -67,3 +67,12 @@ SELECT * FROM t1;
 id	id2
 3	0
 DROP TABLE t1;
+create table t1 (a integer);
+insert into t1 values (1);
+select 1 as a from t1 union all select 1 from dual limit 1;
+a
+1
+(select 1 as a from t1) union all (select 1 from dual) limit 1;
+a
+1
+drop table t1;

mysql-test/t/limit.test

@@ -49,3 +49,13 @@ SELECT * FROM t1;
 DELETE FROM t1 WHERE id2 = 0 ORDER BY id desc LIMIT 1; 
 SELECT * FROM t1;
 DROP TABLE t1;
+
+#
+# Bug#8023 - limit on UNION with from DUAL, causes syntax error
+#
+create table t1 (a integer);
+insert into t1 values (1);
+# both queries must return one row
+select 1 as a from t1 union all select 1 from dual limit 1;
+(select 1 as a from t1) union all (select 1 from dual) limit 1;
+drop table t1;

sql/sql_yacc.yy

@@ -2455,10 +2455,11 @@ select_into:
 select_from:
 	  FROM join_table_list where_clause group_clause having_clause
 	       opt_order_clause opt_limit_clause procedure_clause
-        | FROM DUAL_SYM /* oracle compatibility: oracle always requires FROM
-                           clause, and DUAL is system table without fields.
-                           Is "SELECT 1 FROM DUAL" any better than
-                           "SELECT 1" ? Hmmm :) */
+        | FROM DUAL_SYM opt_limit_clause
+          /* oracle compatibility: oracle always requires FROM clause,
+             and DUAL is system table without fields.
+             Is "SELECT 1 FROM DUAL" any better than "SELECT 1" ?
+          Hmmm :) */
 	;
 
 select_options: