Testing for null value in arrays
I am new to the list and somewhat new to PostgreSQL... so, if my
question seems mundane or trivial I apologize. I have a plpgsql function
that performs multiple inserts and updates on a variety of tables. In
one particular instance the function tests an array for null. If the
array is not null the record is inserted. I can get the array to test
true to null but it fails when reversed.
*** A sample and simple version of what I am trying to do ***
CREATE FUNCTION sb_event_insert (_TEXT)
RETURNS bool
AS 'DECLARE
argv_vector ALIAS FOR $1;
evnt_seq INTEGER;
BEGIN
IF argv_vector = \'{}\'
THEN
evnt_seq := nextval(\'event_sequence\');
INSERT INTO argv VALUES (evnt_seq, argv_vector);
END IF;
END;'
LANGUAGE 'plpgsql';
This evaluates successfully and without errors... but, obviously I am
testing for not null. It seems inefficient to use an IF - THEN - ELSE
statement here. So, by reversing the evaluation
IF argv_vector != \'{}\'
the function when executed fails with the following error:
SELECT sb_event_insert ('{}');
ERROR: Unable to identify an operator '<>' for types '_text' and
'unknown'. You will have to retype this query using an explicit cast.
Regards, Michael Dunn
Michael Dunn <michael@2cactus.com> writes:
IF argv_vector = \'{}\'
THEN
This evaluates successfully and without errors... but, obviously I am
testing for not null.
Um ... no ... you are testing for not-empty-array. A zero-element array
is not the same thing as an SQL NULL. Not sure if the distinction is
important for your purposes or not, but there *is* a difference.
So, by reversing the evaluation
IF argv_vector != \'{}\'
the function when executed fails with the following error:
SELECT sb_event_insert ('{}');
ERROR: Unable to identify an operator '<>' for types '_text' and
'unknown'. You will have to retype this query using an explicit cast.
A moment's poking into pg_operator shows that there is an '=' operator
for text[], but not a '<>' operator:
regression=# select * from pg_operator where oprname = '=' and
regression-# oprleft = (select oid from pg_type where typname = '_text');
oprname | oprowner | oprprec | oprkind | oprisleft | oprcanhash | oprleft | oprright | oprresult | oprcom | oprnegate | oprlsortop | oprrsortop | oprcode | oprrest | oprjoin
---------+----------+---------+---------+-----------+------------+---------+----------+-----------+--------+-----------+------------+------------+----------+---------+-----------
= | 256 | 0 | b | t | f | 1009 | 1009 | 16 | 381 | 0 | 0 | 0 | array_eq | eqsel | eqjoinsel
(1 row)
regression=# select * from pg_operator where oprname = '<>' and
regression-# oprleft = (select oid from pg_type where typname = '_text');
oprname | oprowner | oprprec | oprkind | oprisleft | oprcanhash | oprleft | oprright | oprresult | oprcom | oprnegate | oprlsortop | oprrsortop | oprcode | oprrest | oprjoin
---------+----------+---------+---------+-----------+------------+---------+----------+-----------+--------+-----------+------------+------------+---------+---------+---------
(0 rows)
This is clearly an omission that should be rectified (feel free to
submit a patch!), but it's not exactly catastrophic. Write
"NOT (argv_vector = \'{}\')" if you feel the need to cast your IFs
in that direction.
regards, tom lane