I'm writing a function in PL/pgSQL, and I'm looking for the simplest way to check if a row exists.
Right now I'm SELECTing an integer into a boolean, which doesn't really work. I'm not experienced with PL/pgSQL enough yet to know the best way of doing this.
Here's part of my function:
DECLARE person_exists boolean;
BEGIN
person_exists := FALSE;
SELECT "person_id" INTO person_exists
FROM "people" p
WHERE p.person_id = my_person_id
LIMIT 1;
IF person_exists THEN
-- Do something
END IF;
END; $$ LANGUAGE plpgsql;
Update - I'm doing something like this for now:
DECLARE person_exists integer;
BEGIN
person_exists := 0;
SELECT count("person_id") INTO person_exists
FROM "people" p
WHERE p.person_id = my_person_id
LIMIT 1;
IF person_exists < 1 THEN
-- Do something
END IF;
This question is related to
sql
postgresql
plpgsql
postgresql-9.1
exists
Simpler, shorter, faster: EXISTS.
IF EXISTS (SELECT 1 FROM people p WHERE p.person_id = my_person_id) THEN
-- do something
END IF;
The query planner can stop at the first row found - as opposed to count(), which will scan all matching rows regardless. Makes a difference with big tables. Hardly matters with a condition on a unique column - only one row qualifies anyway (and there is an index to look it up quickly).
Improved with input from @a_horse_with_no_name in the comments below.
You could even use an empty SELECT list:
IF EXISTS (SELECT FROM people p WHERE p.person_id = my_person_id) THEN ...
Since the SELECT list is not relevant to the outcome of EXISTS. Only the existence of at least one qualifying row matters.
Use count(*)
declare
cnt integer;
begin
SELECT count(*) INTO cnt
FROM people
WHERE person_id = my_person_id;
IF cnt > 0 THEN
-- Do something
END IF;
Edit (for the downvoter who didn't read the statement and others who might be doing something similar)
The solution is only effective because there is a where clause on a column (and the name of the column suggests that its the primary key - so the where clause is highly effective)
Because of that where clause there is no need to use a LIMIT or something else to test the presence of a row that is identified by its primary key. It is an effective way to test this.
Source: Stackoverflow.com