카운트 행

Question

나는 Player.country별로 그룹화 reconnect = TRUE와 PlayerSession의 수를 얻기 위해이 쿼리 가지고 :

SELECT 
    country, 
    COUNT(*) AS with_reconnect 
FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id) 
WHERE reconnect = TRUE 
GROUP BY country 

가 난 그냥 다시 연결되지 보여주기 위해 수정하고 싶습니다를 세션 수뿐만 아니라 총 수, 같은 :

SELECT 
    country, 
    COUNT(*) AS total, 
    (COUNT WHERE reconnect = TRUE) AS with_reconnect 
FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id) 
GROUP BY country 

이 경우 가능하며, 그렇다면 적절한 구문은 무엇입니까?

Answer 1

SELECT Country, 
     COUNT(*) AS Total, 
     COUNT(CASE WHEN Reconnect = true THEN 1 END) AS With_Reconnect 
FROM PlayerSession S 
     LEFT JOIN Player P 
      ON P.id = S.player_id 
GROUP BY country 

Answer 2

SELECT 
    country, 
    COUNT(*) AS total, 
    sum(case when reconnect = TRUE then 1 else 0 end) AS with_reconnect 
FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id) 
GROUP BY country 

Answer 3

다음은 그냥 쿼리를 재 작성

SELECT 
    p.country, 
    COUNT(*) AS total, 
    SUM(IF(s.reconnect=TRUE,1,0)) AS with_reconnect 
FROM PlayerSession s 

INNER JOIN Player p 
ON p.id = s.player_id 

GROUP BY p.country 

충분합니다. 모든 PlayerSession에 대해 항상 Player 행이 있으므로이 플레이어가 INNER JOIN으로 변경됩니다. 또한 CONCAT은 (어떤 세션이없는 경우를 제외하고) 항상

Answer 4

SELECT 
    country, 
    COUNT(CASE WHEN reconnect = TRUE THEN S.player_id ELSE NULL END) AS with_reconnect, 
    COUNY(*) 
FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id) 
GROUP BY country