mysql - 计数为 0 的结果未出现

Question

我有一个问题 我需要这个选择给我按内容分组的计数数量

SELECT C.Contenedor, count(DC.Contenedor) as NUM
FROM contenedores AS C, det_contenedores as DC
WHERE C.Contenedor=DC.Contenedor
GROUP BY C.Contenedor

但只出现“count(DC.Contenedor)” > 0 的“C.Contenedor”

结果是(例如):

A->3
B->7
D->6

我想要:

A->3
B->7
C->0
D->6
E->0

有什么想法吗？谢谢!!

Answer 1

您需要使用LEFT JOIN而不是JOIN:

SELECT C.Contenedor, count(DC.Contenedor) as NUM
FROM 
    contenedores AS C 
    LEFT JOIN det_contenedores as DC
        ON C.Contenedor=DC.Contenedor
GROUP BY C.Contenedor