filas contamos con una condición específica en la consulta agregada

Question

tengo esta consulta para obtener el número de PlayerSession s con reconnect = TRUE, agrupados por 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 

me gustaría modificarlo para mostrar no sólo la vuelve a conectar número de sesiones, sino también el recuento total, algo así como:

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 

es esto posible, y si es así, ¿cuál es la sintaxis correcta?

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

El siguiente será suficiente

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 

simplemente Reescribí la consulta. Siempre tendrá una fila de Player por cada PlayerSession, por lo que la cambió para que sea INNER JOIN. Además, no era necesaria la CONCAT como siempre habrá filas PlayerSession en esta consulta (a menos que no hay sesiones)

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