具有LEFT JOIN的表标识符

Question

如何加入 tableD.id = tableC.id AND tableD.id = tableE.id ？ tableD和E都可能有0行，我需要计算它们，即。 SELECT COUNT（E.id）。问题是我不知道在哪里声明表标识符。

我试过了：

FROM tableB B，tableD D，tableE E ...

LEFT JOIN（tableC C，tableD D）ON ...

SELECT B.*, COUNT(C.id) AS cCount 
FROM tableB B
LEFT JOIN (tableC C)
ON (B.id = C.id)
GROUP BY B.id

Answer 1

从你的问题中判断出你在寻找什么是有点困难，但我相信这就是它：

SELECT B.*, COUNT(C.id) AS cCount 
FROM tableB AS B
LEFT JOIN tableC AS C ON B.id = C.id
LEFT JOIN tableD AS D ON C.Id = D.Id
LEFT JOIN tableE AS E ON D.Id = E.Id
GROUP BY B.id