delete inside for plpgsql loop on same relation?
Hi,
Are there guarantees about how this plpgsql behaves? It’s deleting from a table while it loops over it. So far it seems like the delete is logically after the select, as I hoped, and doesn’t interfere.
for row in select * from some_stuff loop
delete from some_stuff where …
...
end loop;
I’m using a temporary table of “things to process” and looping over it, deleting the ones as I go.
I don’t see anything mentioned here: https://www.postgresql.org/docs/11/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING
Rob
Rob Nikander <rob.nikander@gmail.com> writes:
Are there guarantees about how this plpgsql behaves? It’s deleting from a table while it loops over it. So far it seems like the delete is logically after the select, as I hoped, and doesn’t interfere.
for row in select * from some_stuff loop
delete from some_stuff where …
...
end loop;
Sure. A query will not see the effects of queries that start after it.
This isn't particularly plpgsql-specific.
Some qualifications are needed if you have triggers or volatile functions
in the first query (those *can* see later effects); but this usage seems
safe enough.
regards, tom lane