How do I delete a fixed number of rows with sorting in PostgreSQL?

Question

I\'m trying to port some old MySQL queries to PostgreSQL, but I\'m having trouble with this one:

DELETE FROM logtable ORDER BY timestamp LIMIT 10;


        

Answer 1

Postgres docs recommend to use array instead of IN and subquery. This should work much faster

DELETE FROM logtable 
WHERE id = any (array(SELECT id FROM logtable ORDER BY timestamp LIMIT 10));

This and some other tricks can be found here

Answer 2

Assuming you want to delete ANY 10 records (without the ordering) you could do this:

DELETE FROM logtable as t1 WHERE t1.ctid < (select t2.ctid from logtable as t2  where (Select count(*) from logtable t3  where t3.ctid < t2.ctid ) = 10 LIMIT 1);

For my use case, deleting 10M records, this turned out to be faster.

Answer 3

delete from logtable where log_id in (
    select log_id from logtable order by timestamp limit 10);

Answer 4

You could write a procedure which loops over the delete for individual lines, the procedure could take a parameter to specify the number of items you want to delete. But that's a bit overkill compared to MySQL.

Answer 5

You could try using the ctid:

DELETE FROM logtable
WHERE ctid IN (
    SELECT ctid
    FROM logtable
    ORDER BY timestamp
    LIMIT 10
)

The ctid is:

The physical location of the row version within its table. Note that although the ctid can be used to locate the row version very quickly, a row's ctid will change if it is updated or moved by VACUUM FULL. Therefore ctid is useless as a long-term row identifier.

There's also oid but that only exists if you specifically ask for it when you create the table.

Answer 6

If you don't have a primary key you can use the array Where IN syntax with a composite key.

delete from table1 where (schema,id,lac,cid) in (select schema,id,lac,cid from table1 where lac = 0 limit 1000);

This worked for me.