righe contare con una condizione specifica nella query aggregata

Question

ho questa query per ottenere il numero di PlayerSession s con reconnect = TRUE, raggruppati per Player.country:

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 

I desideri modificare per mostrare non solo la ricollegato conteggio della sessione, ma anche il conteggio totale, qualcosa come:

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 

questo è possibile, e se sì, qual è la sintassi corretta?

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

Di seguito sarà sufficiente

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 

Ho appena riscritto la query. Avrai sempre una riga Player per ogni PlayerSession, quindi l'hai cambiata in INNER JOIN. Anche il CONCAT non era necessario, come ci saranno sempre le righe PlayerSession in questa query (a meno che non ci sono sessioni)

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