If your intent is to insert a new record with position incremented by 1,
you should use a trigger. Look at the autoincrement thread from few days
ago.
Markus Bertheau wrote:
Ð ÐÑÑ, 17.08.2004, Ð 16:12, Bruno Wolff III ÐÐÑÐÑ:
SELECT MAX(position) FROM (SELECT position FROM classes WHERE name =
'foo' FOR UPDATE OF classes) AS foo
It's clear which rows should be locked here, I think.
Even if it was allowed, it probably wouldn't be good enough because it won't
protect against newly inserted records.
Can you detail an example where this wouldn't be good enough?
In a PL/pgSQL function I'm doing
PERFORM position FROM class_fields WHERE class = arg_class_name;
INSERT INTO class_fields (class, field, position) VALUES
(arg_class_name, arg_field_name, (SELECT MAX(position) FROM class_fields
WHERE class = arg_class_name));
Is this unsafe?
The question initially arose because I wanted to do something similar to
SELECT INTO var_new_position MAX(position) FROM class_fields WHERE class
= arg_class_name FOR UPDATE OF class_fields;
which didn't work.
Thanks
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