removed wrong distinct UNION detection (BUG#6565)

mysql-test/r/derived.result:
  test of union subquery in the FROM clause with complex distinct/all
mysql-test/t/derived.test:
  test of union subquery in the FROM clause with complex distinct/all
sql/sql_derived.cc:
  removed wrong distinct UNION detection

mysql-test/r/derived.result

@@ -339,3 +339,22 @@ select distinct sum(b) from (select a,b from t1) y group by a;
 sum(b)
 4
 drop table t1;
+create table t1(a int);
+create table t2(a int);
+create table t3(a int);
+insert into t1 values(1),(1);
+insert into t2 values(2),(2);
+insert into t3 values(3),(3);
+select * from t1 union distinct select * from t2 union all select * from t3;
+a
+1
+2
+3
+3
+select * from (select * from t1 union distinct select * from t2 union all select * from t3) X;
+a
+1
+2
+3
+3
+drop table t1, t2, t3;

mysql-test/t/derived.test

@@ -224,3 +224,15 @@ select distinct sum(b) from t1 group by a;
 select distinct sum(b) from (select a,b from t1) y group by a;
 drop table t1;
 
+#
+# test of union subquery in the FROM clause with complex distinct/all (BUG#6565)
+#
+create table t1(a int);
+create table t2(a int);
+create table t3(a int);
+insert into t1 values(1),(1);
+insert into t2 values(2),(2);
+insert into t3 values(3),(3);
+select * from t1 union distinct select * from t2 union all select * from t3;
+select * from (select * from t1 union distinct select * from t2 union all select * from t3) X;
+drop table t1, t2, t3;

sql/sql_derived.cc

@@ -132,10 +132,16 @@ static int mysql_derived(THD *thd, LEX *lex, SELECT_LEX_UNIT *unit,
   /*
     Temp table is created so that it hounours if UNION without ALL is to be 
     processed
+
+    As 'distinct' parameter we always pass FALSE (0), because underlying
+    query will control distinct condition by itself. Correct test of
+    distinct underlying query will be is_union &&
+    !unit->union_distinct->next_select() (i.e. it is union and last distinct
+    SELECT is last SELECT of UNION).
   */
   if (!(table= create_tmp_table(thd, &derived_result->tmp_table_param,
-				unit->types, (ORDER*) 0, 
-				is_union && unit->union_distinct, 1,
+				unit->types, (ORDER*) 0,
+				FALSE, 1,
 				(first_select->options | thd->options |
 				 TMP_TABLE_ALL_COLUMNS),
 				HA_POS_ERROR,