MDEV-6768 Wrong result with aggregate with join with no result set

When a query does implicit grouping and join operation produces an empty
result set, a NULL-complemented row combination is generated.
However, constant table fields still show non-NULL values.

What happens in the is that end_send_group() is called with a
const row but without any rows matching the WHERE clause.
This last part is shown by 'join->first_record' not being set.

This causes item->no_rows_in_result() to be called for all items to reset
all sum functions to their initial state. However fields are not set
to NULL.

The used fix is to produce NULL-complemented records for constant tables
as well. Also, reset the constant table's records back in case we're
in a subquery which may get re-executed.
An alternative fix would have item->no_rows_in_result() also work
with Item_field objects.

There is some other issues with the code:
- join->no_rows_in_result_called is used but never set.
- Tables that are used with group functions are not properly marked as
  maybe_null, which is required if the table rows should be regarded as
  null-complemented (not existing).
- The code that tries to detect if mixed_implicit_grouping should be set
  didn't take into account all usage of fields and sum functions.
- Item_func::restore_to_before_no_rows_in_result() called the wrong
  function.
- join->clear() does not use a table_map argument to clear_tables(),
  which caused it to ignore constant tables.
- unclear_tables() does not correctly restore status to what is
  was before clear_tables().

Main bug fix was to always use a table_map argument to clear_tables() and
always use join->clear() and clear_tables() together with unclear_tables().

Other fixes:
- Fixed Item_func::restore_to_before_no_rows_in_result()
- Set 'join->no_rows_in_result_called' when no_rows_in_result_set()
  is called.
- Removed not used argument from setup_end_select_func().
- More code comments
- Ensure that end_send_group() modifies the same fields as are in the
  result set.
- Changed return_zero_rows() to use pointers instead of references,
  similar to the rest of the code.

Reviewer: Sergei Petrunia <sergey@mariadb.com>

mysql-test/main/group_min_max.result

@@ -4095,5 +4095,115 @@ MIN(pk)	a
 5	10
 DROP TABLE t1;
 #
+# MDEV-6768 Wrong result with agregate with join with no resultset
+#
+create table t1
+(
+PARENT_ID int(10) unsigned NOT NULL AUTO_INCREMENT,
+PARENT_FIELD VARCHAR(10),
+PRIMARY KEY (PARENT_ID)
+) engine=innodb;
+create table t2
+(
+CHILD_ID INT NOT NULL AUTO_INCREMENT,
+PARENT_ID INT NOT NULL,
+CHILD_FIELD varchar(10),
+PRIMARY KEY (CHILD_ID)
+)engine=innodb;
+INSERT INTO t1 (PARENT_FIELD)
+SELECT 'AAAA';
+INSERT INTO t2 (PARENT_ID, CHILD_FIELD)
+SELECT 1, 'BBBB';
+explain select
+t1.PARENT_ID,
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	1	Using where
+select
+t1.PARENT_ID,
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+PARENT_ID	min(CHILD_FIELD)
+NULL	NULL
+select
+1,
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+1	min(CHILD_FIELD)
+1	NULL
+select
+IFNULL(t1.PARENT_ID,1),
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+IFNULL(t1.PARENT_ID,1)	min(CHILD_FIELD)
+1	NULL
+# Check that things works with MyISAM (which has different explain)
+alter table t1 engine=myisam;
+alter table t2 engine=myisam;
+explain select
+t1.PARENT_ID,
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE noticed after reading const tables
+select
+t1.PARENT_ID,
+min(CHILD_FIELD)
+from t1 straight_join t2
+where t1.PARENT_ID = 1
+and t1.PARENT_ID = t2.PARENT_ID
+and t2.CHILD_FIELD = "ZZZZ";
+PARENT_ID	min(CHILD_FIELD)
+NULL	NULL
+drop table t1,t2;
+# Check that things works if sub queries are re-executed
+create table t1 (a int primary key, b int);
+create table t2 (a int primary key, b int);
+create table t3 (a int primary key, b int);
+insert into t1 values (1,1),(2,2),(3,3);
+insert into t2 values (1,1),(2,2),(3,3);
+insert into t3 values (1,1),(3,3);
+explain
+select *,
+(select
+CONCAT('t2:',       IFNULL(t2.a,      't2a-null'), ';',
+'min_t3_b:', IFNULL(min(t3.b), 't3b-null'))
+from t2,t3
+where t2.a=1 and t1.b = t3.a) as s1
+from t1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
+2	DEPENDENT SUBQUERY	t2	const	PRIMARY	PRIMARY	4	const	1	Using index
+2	DEPENDENT SUBQUERY	t3	eq_ref	PRIMARY	PRIMARY	4	test.t1.b	1	
+select *,
+(select
+CONCAT('t2:',       IFNULL(t2.a,      't2a-null'), ';',
+'min_t3_b:', IFNULL(min(t3.b), 't3b-null'))
+from t2,t3
+where t2.a=1 and t1.b = t3.a) as s1
+from t1;
+a	b	s1
+1	1	t2:1;min_t3_b:1
+2	2	t2:t2a-null;min_t3_b:t3b-null
+3	3	t2:1;min_t3_b:3
+drop table t1,t2,t3;
+#
 # End of 10.5 tests
 #

mysql-test/main/group_min_max.test

@@ -1748,6 +1748,116 @@ SELECT MIN(pk), a FROM t1 WHERE pk <> 1 GROUP BY a;
 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-6768 Wrong result with agregate with join with no resultset
+--echo #
+
+create table t1
+(
+	PARENT_ID int(10) unsigned NOT NULL AUTO_INCREMENT,
+	PARENT_FIELD VARCHAR(10),
+	PRIMARY KEY (PARENT_ID)
+) engine=innodb;
+
+create table t2
+(
+	CHILD_ID INT NOT NULL AUTO_INCREMENT,
+	PARENT_ID INT NOT NULL,
+	CHILD_FIELD varchar(10),
+	PRIMARY KEY (CHILD_ID)
+)engine=innodb;
+
+INSERT INTO t1 (PARENT_FIELD)
+SELECT 'AAAA';
+
+INSERT INTO t2 (PARENT_ID, CHILD_FIELD)
+SELECT 1, 'BBBB';
+
+explain select
+ t1.PARENT_ID,
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+select
+ t1.PARENT_ID,
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+select
+ 1,
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+select
+ IFNULL(t1.PARENT_ID,1),
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+
+--echo # Check that things works with MyISAM (which has different explain)
+
+alter table t1 engine=myisam;
+alter table t2 engine=myisam;
+
+explain select
+ t1.PARENT_ID,
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+select
+ t1.PARENT_ID,
+ min(CHILD_FIELD)
+ from t1 straight_join t2
+ where t1.PARENT_ID = 1
+ and t1.PARENT_ID = t2.PARENT_ID
+ and t2.CHILD_FIELD = "ZZZZ";
+
+drop table t1,t2;
+
+--echo # Check that things works if sub queries are re-executed
+
+create table t1 (a int primary key, b int);
+create table t2 (a int primary key, b int);
+create table t3 (a int primary key, b int);
+
+insert into t1 values (1,1),(2,2),(3,3);
+insert into t2 values (1,1),(2,2),(3,3);
+insert into t3 values (1,1),(3,3);
+
+explain
+select *,
+   (select
+        CONCAT('t2:',       IFNULL(t2.a,      't2a-null'), ';',
+               'min_t3_b:', IFNULL(min(t3.b), 't3b-null'))
+    from t2,t3
+    where t2.a=1 and t1.b = t3.a) as s1
+from t1;
+
+select *,
+   (select
+        CONCAT('t2:',       IFNULL(t2.a,      't2a-null'), ';',
+               'min_t3_b:', IFNULL(min(t3.b), 't3b-null'))
+    from t2,t3
+    where t2.a=1 and t1.b = t3.a) as s1
+from t1;
+
+drop table t1,t2,t3;
+
 --echo #
 --echo # End of 10.5 tests
 --echo #

mysql-test/main/type_timestamp.result

@@ -1230,6 +1230,8 @@ SELECT * FROM t1 HAVING MIN(t1.c1) >= ALL(SELECT 'a' UNION SELECT 'r');
 c1
 Warnings:
 Warning	1292	Truncated incorrect datetime value: 'r'
+SELECT * FROM t1 HAVING MIN(t1.c1) > 0;
+c1
 DROP TABLE t1;
 CREATE TABLE t1 (c1 timestamp);
 INSERT INTO t1 VALUES ('2010-01-01 00:00:00');

mysql-test/main/type_timestamp.test

@@ -810,6 +810,7 @@ DROP TABLE t1;
 CREATE TABLE t1 (c1 timestamp);
 SELECT MIN(t1.c1) AS k1 FROM t1 HAVING (k1 >= ALL(SELECT 'a' UNION SELECT 'r'));
 SELECT * FROM t1 HAVING MIN(t1.c1) >= ALL(SELECT 'a' UNION SELECT 'r');
+SELECT * FROM t1 HAVING MIN(t1.c1) > 0;
 DROP TABLE t1;
 
 CREATE TABLE t1 (c1 timestamp);

sql/item_func.h

@@ -380,7 +380,7 @@ class Item_func :public Item_func_or_sum,
   {
     for (uint i= 0; i < arg_count; i++)
     {
-      args[i]->no_rows_in_result();
+      args[i]->restore_to_before_no_rows_in_result();
     }
   }
   void convert_const_compared_to_int_field(THD *thd);

sql/sql_select.h

@@ -227,7 +227,7 @@ enum sj_strategy_enum
 
 typedef enum_nested_loop_state
 (*Next_select_func)(JOIN *, struct st_join_table *, bool);
-Next_select_func setup_end_select_func(JOIN *join, JOIN_TAB *tab);
+Next_select_func setup_end_select_func(JOIN *join);
 int rr_sequential(READ_RECORD *info);
 int rr_sequential_and_unpack(READ_RECORD *info);
 Item *remove_pushed_top_conjuncts(THD *thd, Item *cond);
@@ -1767,7 +1767,8 @@ class JOIN :public Sql_alloc
   void join_free();
   /** Cleanup this JOIN, possibly for reuse */
   void cleanup(bool full);
-  void clear();
+  void clear(table_map *cleared_tables);
+  void inline clear_sum_funcs();
   bool send_row_on_empty_set()
   {
     return (do_send_rows && implicit_grouping && !group_optimized_away &&

sql/table.h

@@ -3306,10 +3306,16 @@ inline void mark_as_null_row(TABLE *table)
     bfill(table->null_flags,table->s->null_bytes,255);
 }
 
+/*
+  Restore table to state before mark_as_null_row() call.
+  This assumes that the caller has restored table->null_flags,
+  as is done in unclear_tables().
+*/
+
 inline void unmark_as_null_row(TABLE *table)
 {
-  table->null_row=0;
-  table->status= STATUS_NO_RECORD;
+  table->null_row= 0;
+  table->status&= ~STATUS_NULL_ROW;
 }
 
 bool is_simple_order(ORDER *order);