カウント行

Question

私はPlayer.countryごとにグループ化され、reconnect = TRUEとPlayerSession秒数を取得するには、このクエリを持っている：

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 

私が再接続だけではなくを表示するように変更したいのですがセッション数だけでなく、合計数などを入力します。

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 

これが可能ですか？その場合、正しい構文は何ですか？

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

以下は、私は、クエリを書き直し

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 

十分でしょう。 PlayerSessionごとにPlayerの行が常にあるため、INNER JOINに変更されます。また、常にPlayerSession行がこのクエリであるだろうと必要に応じていませんでしたCONCAT（セッションがない限り）

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