Add LIMIT to query with LEFT JOIN and DELETE in PostgreSQL

Question

I'm trying to delete data from a table that has about 12 million records, wanting to delete it in batches but you can't use LIMIT with DELETE in sql, I'm a bit stumped on how to get around it.

The query without LIMIT is:

DELETE FROM roster_validationtaskerror
USING roster_validationtaskerror AS rvte
LEFT JOIN roster_validationtask AS rvt ON rvt.id = rvte.parent_task_id
LEFT JOIN roster_validation AS rv ON rv.id = rvt.validation_id
WHERE rv.id = 10

How can I add a LIMIT to this query?

I've been trying to add subselect queries to allow for the LIMIT to be added within this and then a JOIN made after. I'm quite new to SQL so have not been able to figure out how to get this to work.

Answer 1

Try this:

WITH r AS (
    SELECT rvte.id 
    FROM roster_validationtaskerror AS rvte
    JOIN roster_validationtask AS rvt ON rvt.id = rvte.parent_task_id
    JOIN roster_validation AS rv ON rv.id = rvt.validation_id
    WHERE rv.id = 10
    -- perhaps order by is needed if you want to delete not randomly selected rows
    LIMIT 10
)
DELETE FROM roster_validationtaskerror
USING r
WHERE r.id = roster_validationtaskerror.id