MDEV-10763: Wrong result - server does not return NULL values from default list partition after ALTER table

Fixed partition pruning for NULL value.

Author: sanja-byelkin

mysql-test/r/partition_default.result

@@ -1204,3 +1204,32 @@ where a>=10  and (a <=10 and b <=30);
 id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	p1,p2,p3	ALL	NULL	NULL	NULL	NULL	3	Using where
 drop table t1;
+#
+# MDEV-10763: Wrong result - server does not return NULL values
+# from default list partition after ALTER table
+#
+create table t1 (i int) partition by list (i) ( partition p1 default);
+insert into t1 values (null);
+select * from t1 where i is null;
+i
+NULL
+alter table t1 partition by list (i) ( partition p1 values in (1), partition p2 default);
+select * from t1 where i is null;
+i
+NULL
+explain partitions 
+select * from t1 where i is null;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	p2	system	NULL	NULL	NULL	NULL	1	
+alter table t1 partition by list (i) (
+partition p0 values in (NULL),
+partition p1 values in (1),
+partition p2 default);
+select * from t1 where i is null;
+i
+NULL
+explain partitions 
+select * from t1 where i is null;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	p0	system	NULL	NULL	NULL	NULL	1	
+drop table t1;

mysql-test/t/partition_default.test

@@ -498,5 +498,25 @@ insert into t1 values
 explain partitions 
 select * from t1 
 where a>=10  and (a <=10 and b <=30);
+drop table t1;
+
+--echo #
+--echo # MDEV-10763: Wrong result - server does not return NULL values
+--echo # from default list partition after ALTER table
+--echo #
+create table t1 (i int) partition by list (i) ( partition p1 default);
+insert into t1 values (null);
+select * from t1 where i is null;
+alter table t1 partition by list (i) ( partition p1 values in (1), partition p2 default);
+select * from t1 where i is null;
+explain partitions 
+select * from t1 where i is null;
+alter table t1 partition by list (i) (
+  partition p0 values in (NULL),
+  partition p1 values in (1),
+  partition p2 default);
+select * from t1 where i is null;
+explain partitions 
+select * from t1 where i is null;
 
 drop table t1;

sql/sql_partition.cc

@@ -7960,8 +7960,19 @@ int get_part_iter_for_interval_via_mapping(partition_info *part_info,
         /* col = x and F(x) = NULL -> only search NULL partition */
         part_iter->part_nums.cur= part_iter->part_nums.start= 0;
         part_iter->part_nums.end= 0;
-        part_iter->ret_null_part= part_iter->ret_null_part_orig= TRUE;
-        DBUG_RETURN(1);
+        /*
+          if NULL partition exists:
+            for RANGE it is the first partition (always exists);
+            for LIST should be indicator that it is present
+        */
+        if (part_info->part_type == RANGE_PARTITION ||
+            part_info->has_null_value)
+        {
+          part_iter->ret_null_part= part_iter->ret_null_part_orig= TRUE;
+          DBUG_RETURN(1);
+        }
+        // If no NULL partition look up in DEFAULT or there is no such value
+        goto not_found;
       }
       part_iter->part_nums.cur= part_iter->part_nums.start;
       if (check_zero_dates && !part_info->part_expr->null_value)