MDEV-37407 Wrong result with LATERAL DERIVED

This is backported from MDEV-37057 for MariaDB 10.11

When populating the structure spl_opt_info for a TABLE, and evaluating a
key_field for inclusion in spl_opt_info->added_key_fields, the null_rejecting
attribute may be incorrectly set.  Originally, this attribute was
assumed to be TRUE, then it was changed

  Item *real= key_field->val->real_item();
  if ((real->type() == Item::FIELD_ITEM) &&
        ((Item_field*)real)->field->maybe_null())
    added_key_field->null_rejecting= true;
  else
    added_key_field->null_rejecting= false;

which also incorrectly assumed that the added key field depended on
whether the field was able to set to null.

The correct setting for this attribute is simply to pass it through from
the key being evaluated.

The result of an incorrect value is, in this test case, incorrect
equality conditions being pushed into our (lateral) derived table,
excluding rows that might legitimately contain NULL and thus returning
a wrong result.

Reviewed by Dave Gosselin (dave.gosselin@mariadb.com), PR#4236

Author: mariadb-RexJohnston

mysql-test/main/derived_split_innodb.result

@@ -967,5 +967,40 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 2	DERIVED	t10	index	grp_id	grp_id	5	NULL	10000	Using index; Using temporary; Using filesort
 drop table t1,t2, t10;
 drop view v1;
+#
+# MDEV-37407 Wrong result with LATERAL DERIVED
+#
+CREATE TABLE t1 (
+a int NOT NULL,
+b int default null,
+amount decimal DEFAULT NULL,
+KEY t1_IDX (a,b) USING BTREE
+) ENGINE=INNODB;
+CREATE TABLE t2 (
+a int NOT NULL,
+b int default null,
+name varchar(50) DEFAULT NULL,
+KEY t2_IDX (a,b) USING BTREE
+) ENGINE=INNODB;
+INSERT INTO t1 VALUES
+(1, NULL, 10.0000), (2, 2, 20.0000), (3, 3, 30.0000), (4, 4, 40.0000),
+(5, 5, NULL), (6, 6, NULL), (7, 7, 70.0000), (8, 8, 80.0000);
+INSERT INTO t2 VALUES
+(1, NULL, 'A'), (2,2, 'B'), (3,3, 'C'), (4,4, 'D'), (5,5, NULL), (6,6, NULL),
+(7,7, 'E'), (8,8, 'F'), (9,9, 'G'), (10,10,'H'), (11,11, NULL), (12,12, NULL);
+# Must use Split-Materialized:
+explain $query;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	t2	range	t2_IDX	t2_IDX	4	NULL	1	Using index condition
+1	PRIMARY	<derived2>	ref	key0	key0	10	test.t2.a,test.t2.b	2	Using where
+2	LATERAL DERIVED	t1	ref	t1_IDX	t1_IDX	9	test.t2.a,test.t2.b	1	
+$query;
+a	b	name	total_amt
+1	NULL	A	10
+# Compare with correct result:
+set statement optimizer_switch='split_materialized=off' for $query;
+a	b	name	total_amt
+1	NULL	A	10
+DROP TABLE t1,t2;
 # End of 10.11 tests
 SET GLOBAL innodb_stats_persistent=@save_innodb_stats_persistent;

mysql-test/main/derived_split_innodb.test

@@ -578,5 +578,47 @@ where
 drop table t1,t2, t10;
 drop view v1;
 
+--echo #
+--echo # MDEV-37407 Wrong result with LATERAL DERIVED
+--echo #
+
+CREATE TABLE t1 (
+  a int NOT NULL,
+  b int default null,
+  amount decimal DEFAULT NULL,
+  KEY t1_IDX (a,b) USING BTREE
+) ENGINE=INNODB;
+
+CREATE TABLE t2 (
+  a int NOT NULL,
+  b int default null,
+  name varchar(50) DEFAULT NULL,
+  KEY t2_IDX (a,b) USING BTREE
+) ENGINE=INNODB;
+
+INSERT INTO t1 VALUES
+(1, NULL, 10.0000), (2, 2, 20.0000), (3, 3, 30.0000), (4, 4, 40.0000),
+(5, 5, NULL), (6, 6, NULL), (7, 7, 70.0000), (8, 8, 80.0000);
+
+INSERT INTO t2 VALUES
+(1, NULL, 'A'), (2,2, 'B'), (3,3, 'C'), (4,4, 'D'), (5,5, NULL), (6,6, NULL),
+(7,7, 'E'), (8,8, 'F'), (9,9, 'G'), (10,10,'H'), (11,11, NULL), (12,12, NULL);
+
+let $query=
+SELECT t2.a,t2.b,t2.name,t.total_amt FROM t2
+LEFT JOIN
+(
+  SELECT a, b, sum(amount) total_amt FROM t1 GROUP BY a, b
+) AS t ON t2.a=t.a and t2.b<=>t.b
+WHERE t2.a < 2;
+
+--echo # Must use Split-Materialized:
+evalp explain $query;
+evalp $query;
+--echo # Compare with correct result:
+evalp set statement optimizer_switch='split_materialized=off' for $query;
+
+DROP TABLE t1,t2;
+
 --echo # End of 10.11 tests
 SET GLOBAL innodb_stats_persistent=@save_innodb_stats_persistent;

sql/opt_split.cc

@@ -630,14 +630,7 @@ void TABLE::add_splitting_info_for_key_field(KEY_FIELD *key_field)
   added_key_field->level= 0;
   added_key_field->optimize= KEY_OPTIMIZE_EQ;
   added_key_field->eq_func= true;
-
-  Item *real= key_field->val->real_item();
-  if ((real->type() == Item::FIELD_ITEM) &&
-        ((Item_field*)real)->field->maybe_null())
-    added_key_field->null_rejecting= true;
-  else
-    added_key_field->null_rejecting= false;
-
+  added_key_field->null_rejecting= key_field->null_rejecting;
   added_key_field->cond_guard= NULL;
   added_key_field->sj_pred_no= UINT_MAX;
   return;