Fix for bug #1727 ( Crash in EXPLAIN & UNION & derived)

another version of the fix.
Here i removed a loop that seems to be superfluous

mysql-test/r/derived.result

@@ -228,3 +228,20 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
 3	DEPENDENT SUBQUERY	B	ALL	NULL	NULL	NULL	NULL	2	Using where
 drop table t1;
+create table t1 (a int);
+insert into t1 values (1),(2);
+select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
+a	a
+1	1
+2	1
+1	2
+2	2
+explain select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	<derived2>	ALL	NULL	NULL	NULL	NULL	2	
+1	PRIMARY	<derived4>	ALL	NULL	NULL	NULL	NULL	2	
+4	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	
+5	UNION	t1	ALL	NULL	NULL	NULL	NULL	2	
+2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	2	
+3	UNION	t1	ALL	NULL	NULL	NULL	NULL	2	
+drop table t1;

mysql-test/t/derived.test

@@ -132,3 +132,9 @@ insert into t1 VALUES(1,1,1), (2,2,1);
 select count(*) from t1 INNER JOIN (SELECT A.E1, A.E2, A.E3 FROM t1 AS A WHERE A.E3 = (SELECT MAX(B.E3) FROM t1 AS B WHERE A.E2 = B.E2)) AS THEMAX ON t1.E1 = THEMAX.E2 AND t1.E1 = t1.E2;
 explain select count(*) from t1 INNER JOIN (SELECT A.E1, A.E2, A.E3 FROM t1 AS A WHERE A.E3 = (SELECT MAX(B.E3) FROM t1 AS B WHERE A.E2 = B.E2)) AS THEMAX ON t1.E1 = THEMAX.E2 AND t1.E1 = t1.E2;
 drop table t1;
+
+create table t1 (a int);
+insert into t1 values (1),(2);
+select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
+explain select * from ( select * from t1 union select * from t1) a,(select * from t1 union select * from t1) b;
+drop table t1;

sql/sql_lex.cc

@@ -1269,28 +1269,6 @@ bool st_select_lex::test_limit()
   return(0);
 }
 
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 /*  
   Interface method of table list creation for query
   
@@ -1315,13 +1293,8 @@ bool st_select_lex_unit::create_total_list(THD *thd, st_lex *lex,
 					   bool check_derived)
 {
   *result= 0;
-  for (SELECT_LEX_UNIT *unit= this; unit; unit= unit->next_unit())
-  {
-    if ((res= unit->create_total_list_n_last_return(thd, lex, &result,
-						    check_derived)))
-      return res;
-  }
-  return 0;
+  res= create_total_list_n_last_return(thd, lex, &result, check_derived);
+  return res;
 }
 
 /*