From: | Yaroslav <ladayaroslav(at)yandex(dot)ru> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: CTE inlining |
Date: | 2017-05-11 21:37:27 |
Message-ID: | 1494538647075-5961086.post@n3.nabble.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Ilya Shkuratov wrote
> First of all, to such replacement to be valid, the CTE must be
> 1. non-writable (e.g. be of form: SELECT ...),
> 2. do not use VOLATILE or STABLE functions,
> 3. ... (maybe there must be more restrictions?)
What about simple things like this?
CREATE OR REPLACE FUNCTION z(numeric) RETURNS boolean AS $$
BEGIN
RETURN $1 <> 0;
END;
$$ LANGUAGE plpgSQL IMMUTABLE COST 1000;
-- This one works:
WITH T AS (
SELECT 1.0 AS v1, 0.0 AS v2
UNION ALL
SELECT 3.0, 1.0
UNION ALL
SELECT 2.0, 0.0
), a AS (
SELECT *
FROM t
WHERE z(v2)
)
SELECT *
FROM a
WHERE v1/v2 > 1.5;
-- This one gives 'division by zero':
WITH T AS (
SELECT 1.0 AS v1, 0.0 AS v2
UNION ALL
SELECT 3.0, 1.0
UNION ALL
SELECT 2.0, 0.0
)
SELECT *
FROM (
SELECT *
FROM t
WHERE z(v2)
) AS a
WHERE v1/v2 > 1.5;
-----
WBR, Yaroslav Schekin.
--
View this message in context: http://www.postgresql-archive.org/CTE-inlining-tp5958992p5961086.html
Sent from the PostgreSQL - hackers mailing list archive at Nabble.com.
From | Date | Subject | |
---|---|---|---|
Next Message | Andres Freund | 2017-05-11 21:51:55 | Re: snapbuild woes |
Previous Message | Andres Freund | 2017-05-11 21:28:39 | Re: [HACKERS] Concurrent ALTER SEQUENCE RESTART Regression |