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I'm trying to make a function in PostgreSQL which returns true or false if a row exist. It's very easy in SQL, and performance is good:

SELECT exists (SELECT 1
 FROM Users u
 WHERE u.id = $1)

But when I try to create a function with this code, the performance is terrible:

CREATE OR REPLACE FUNCTION userExist(userId integer) 
RETURNS boolean AS $$ 
 SELECT exists (SELECT 1
     FROM User u
     WHERE u.id = $1);
 $$ LANGUAGE sql STABLE;

I call this function like that : 

EXPLAIN ANALYZE SELECT * FROM userExist(1);

Seems that the problem is the same as a previous question I ask ( PostgreSQL Performance - SELECT vs Stored function ), but the answer i get last time doesn't work in this situation.

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2
  • You have a scalar function which returns a single value. Don't put that in the from clause, use select userexist(1); Commented Jun 24, 2015 at 15:39
  • Ok, otherwise performance are exactly the same with or without the from Commented Jun 24, 2015 at 15:45
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