Saml kolonner med yderligere (særskilte) filtre

Det samlede FILTER klausul i Postgres 9.4 eller nyere er kortere og hurtigere:

SELECT u.name
     , count(*) FILTER (WHERE g.winner_id  > 0)    AS played
     , count(*) FILTER (WHERE g.winner_id  = u.id) AS won
     , count(*) FILTER (WHERE g.winner_id <> u.id) AS lost
FROM   games g
JOIN   users u ON u.id IN (g.player_1_id, g.player_2_id)
GROUP  BY u.name;

• Manualen
• Postgres Wiki
• Depesz blogindlæg

I Postgres 9.3 (eller enhver version) dette er stadig kortere og hurtigere end indlejrede undervalg eller CASE udtryk:

SELECT u.name
     , count(g.winner_id  > 0 OR NULL)    AS played
     , count(g.winner_id  = u.id OR NULL) AS won
     , count(g.winner_id <> u.id OR NULL) AS lost
FROM   games g
JOIN   users u ON u.id IN (g.player_1_id, g.player_2_id)
GROUP  BY u.name;

Detaljer:

• Er SUM hurtigere eller COUNT for absolut ydeevne?