[MDEV-30099] DELETE .. RETURNING does not always return metadata Created: 2022-11-25  Updated: 2023-11-28

Status: Open
Project: MariaDB Server
Component/s: Data Manipulation - Delete
Affects Version/s: 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 10.10, 10.11
Fix Version/s: 10.4, 10.5, 10.6

Type: Bug Priority: Major
Reporter: Elena Stepanova Assignee: Rucha Deodhar
Resolution: Unresolved Votes: 0
Labels: None


 Description   

In some cases DELETE ... RETURNING which does not delete any rows does not return metadata. In other cases it does. Apparently it is not the expected behavior/

create table t (a int);
 
--enable_metadata
 
delete from t returning *;
 
delete from t where 0 returning *;
 
delete from t where not exists (select * from mysql.user) returning *;
 
select * from t where 0;
 
 
 
# Cleanup
 
--disable_metadata
 
drop table t;

10.3 162c1505

 
delete from t returning *;
 
Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
 
def	test	t	t	a	a	3	11	0	Y	32768	0	63
 
a
 
delete from t where 0 returning *;
 
delete from t where not exists (select * from mysql.user) returning *;
 
select * from t where 0;
 
Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
 
def	test	t	t	a	a	3	11	0	Y	32768	0	63
 
a

So, DELETE without a WHERE clause returns metadata, even though the table is empty. But DELETE with an impossible condition does not.
SELECT however returns metadata with the same impossible conditions.
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