MDEV-10172: UNION query returns incorrect rows outside conditional evaluation

count duplicate of UNION SELECT separately to awoid influence on lokal LIMIT clause.

mysql-test/r/union.result

@@ -362,7 +362,7 @@ a
 2
 select found_rows();
 found_rows()
-6
+5
 SELECT SQL_CALC_FOUND_ROWS * FROM t1 UNION SELECT * FROM t2 LIMIT 100;
 a
 1
@@ -1169,12 +1169,9 @@ a	b
 select * from ((select * from t1 limit 1) union (select * from t1 limit 1)) a;
 a	b
 1	a
-2	b
 select * from ((select * from t1 limit 1) union (select * from t1 limit 1) union (select * from t1 limit 1)) a;
 a	b
 1	a
-2	b
-3	c
 select * from ((((select * from t1))) union (select * from t1) union (select * from t1)) a;
 a	b
 1	a
@@ -1553,7 +1550,6 @@ NULL	UNION RESULT	<union1,2>	ALL	NULL	NULL	NULL	NULL	NULL	NULL	Using filesort
 Warnings:
 Note	1003	select NULL AS `a` from `test`.`t1` union select NULL AS `a` from `test`.`t1` order by `a`
 DROP TABLE t1;
-End of 5.0 tests
 #
 # Bug#32858: Error: "Incorrect usage of UNION and INTO" does not take 
 # subselects into account
@@ -1659,6 +1655,14 @@ a
 4
 5
 6
+(select a from t1 where false) UNION (select a from t1) limit 8;
+a
+10
+2
+3
+4
+5
+6
 7
 8
 drop table t1;
@@ -1955,3 +1959,22 @@ cccc
 bbbb
 dddd
 drop table t1;
+#
+# MDEV-10172: UNION query returns incorrect rows outside
+# conditional evaluation
+#
+create table t1 (d datetime not null primary key);
+insert into t1(d) values ('2016-06-01'),('2016-06-02'),('2016-06-03'),('2016-06-04');
+select * from
+(
+select * from t1 where d between '2016-06-02' and '2016-06-05'
+	union
+(select * from t1 where d < '2016-06-05' order by d desc limit 1)
+) onlyJun2toJun4
+order by d;
+d
+2016-06-02 00:00:00
+2016-06-03 00:00:00
+2016-06-04 00:00:00
+drop table t1;
+End of 5.0 tests

mysql-test/t/union.test

@@ -1022,7 +1022,6 @@ ORDER BY a;
 DROP TABLE t1;
 
 
---echo End of 5.0 tests
 -- echo #
 -- echo # Bug#32858: Error: "Incorrect usage of UNION and INTO" does not take 
 -- echo # subselects into account
@@ -1126,6 +1125,8 @@ create table t1 (a int);
 insert into t1 values (10),(10),(10),(2),(3),(4),(5),(6),(7),(8),(9),(1),(10);
 --sorted_result
 select a from t1 where false UNION select a from t1 limit 8;
+--sorted_result
+(select a from t1 where false) UNION (select a from t1) limit 8;
 drop table t1;
 
 --echo #
@@ -1350,3 +1351,22 @@ UNION
 ;
 
 drop table t1;
+
+
+--echo #
+--echo # MDEV-10172: UNION query returns incorrect rows outside
+--echo # conditional evaluation
+--echo #
+
+create table t1 (d datetime not null primary key);
+insert into t1(d) values ('2016-06-01'),('2016-06-02'),('2016-06-03'),('2016-06-04');
+select * from
+(
+	select * from t1 where d between '2016-06-02' and '2016-06-05'
+	union
+	(select * from t1 where d < '2016-06-05' order by d desc limit 1)
+) onlyJun2toJun4
+order by d;
+drop table t1;
+
+--echo End of 5.0 tests

sql/sql_select.cc

@@ -2871,7 +2871,7 @@ JOIN::exec()
                                     *curr_fields_list),
                                    Protocol::SEND_NUM_ROWS | Protocol::SEND_EOF);
   error= do_select(curr_join, curr_fields_list, NULL, procedure);
-  thd->limit_found_rows= curr_join->send_records;
+  thd->limit_found_rows= curr_join->send_records - curr_join->duplicate_rows;
 
   /* Accumulate the counts from all join iterations of all join parts. */
   thd->examined_row_count+= curr_join->examined_rows;
@@ -16578,7 +16578,7 @@ do_select(JOIN *join,List<Item> *fields,TABLE *table,Procedure *procedure)
     join->join_tab[join->top_join_tab_count - 1].next_select= end_select;
     join_tab=join->join_tab+join->const_tables;
   }
-  join->send_records=0;
+  join->duplicate_rows= join->send_records=0;
   if (join->table_count == join->const_tables)
   {
     /*
@@ -18089,7 +18089,12 @@ end_send(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
       int error;
       /* result < 0 if row was not accepted and should not be counted */
       if ((error= join->result->send_data(*join->fields)))
-        DBUG_RETURN(error < 0 ? NESTED_LOOP_OK : NESTED_LOOP_ERROR);
+      {
+        if (error > 0)
+          DBUG_RETURN(NESTED_LOOP_ERROR);
+        // error < 0 => duplicate row
+        join->duplicate_rows++;
+      }
     }
     if (++join->send_records >= join->unit->select_limit_cnt &&
 	join->do_send_rows)
@@ -18205,7 +18210,7 @@ end_send_group(JOIN *join, JOIN_TAB *join_tab __attribute__((unused)),
               if (error < 0)
               {
                 /* Duplicate row, don't count */
-                join->send_records--;
+                join->duplicate_rows++;
                 error= 0;
               }
             }

sql/sql_select.h

@@ -1018,7 +1018,8 @@ class JOIN :public Sql_alloc
   table_map outer_join;
   /* Bitmap of tables used in the select list items */
   table_map select_list_used_tables;
-  ha_rows  send_records,found_records,examined_rows,row_limit, select_limit;
+  ha_rows  send_records, found_records, examined_rows,
+           row_limit, select_limit, duplicate_rows;
   /**
     Used to fetch no more than given amount of rows per one
     fetch operation of server side cursor.
@@ -1272,7 +1273,7 @@ class JOIN :public Sql_alloc
     sort_and_group= 0;
     first_record= 0;
     do_send_rows= 1;
-    send_records= 0;
+    duplicate_rows= send_records= 0;
     found_records= 0;
     fetch_limit= HA_POS_ERROR;
     examined_rows= 0;