Re: Query runs too long for indexed tables

> outer joins are not supported in Postgres UPDATE command.

    True (and sad).

    You can try the following script to play with the various options :


DROP TABLE one;
DROP TABLE two;

CREATE TABLE one (a SERIAL PRIMARY KEY, b INT NULL);
CREATE TABLE two (b INT NOT NULL PRIMARY KEY);
INSERT INTO two (b) SELECT x*2 FROM generate_series( 1, 50000 ) AS x;
INSERT INTO one (b) SELECT x FROM generate_series( 1, 100000 ) AS x;

EXPLAIN ANALYZE SELECT count(*) FROM one LEFT JOIN two ON one.b=two.b
WHERE two.b IS NULL;

--Try with and without...
--CREATE INDEX one_b ON one(b);

VACUUM ANALYZE one;
VACUUM ANALYZE two;

EXPLAIN ANALYZE SELECT count(*) FROM one LEFT JOIN two ON one.b=two.b
WHERE two.b IS NULL;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=NULL WHERE b NOT IN (SELECT b FROM two );
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=NULL WHERE b IN (SELECT one.b FROM one
LEFT JOIN two ON one.b=two.b WHERE two.b IS NULL);
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=NULL FROM one x LEFT JOIN two ON
x.b=two.b WHERE two.b IS NULL AND one.a=x.a;
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=NULL FROM one x LEFT JOIN two ON
x.b=two.b WHERE two.b IS NULL AND one.b=x.b;
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=(SELECT two.b FROM two WHERE two.b=one.b);
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
EXPLAIN ANALYZE UPDATE one SET b=NULL WHERE NOT EXISTS (SELECT 1 FROM two
WHERE two.b = one.b);
SELECT * FROM one ORDER BY a LIMIT 5;
ROLLBACK;
VACUUM one;

BEGIN;
CREATE TABLE tmp AS SELECT one.a, two.b FROM one LEFT JOIN two ON
one.b=two.b;
SELECT * FROM tmp ORDER BY a LIMIT 5;
DROP TABLE one;
ALTER TABLE tmp RENAME TO one;
ROLLBACK;