Mysql 内部连接两次并在两次连接上使用 WHERE

Question

在 MySQL 中，我想 SELECT A.* FROM A 满足内部连接条件，无论是直接(连接表 B)还是 通过另一个连接表 (C)，WHERE B.field = myvalue。谁能指出获得结果的正确方法？

我有以下表:A、B、C，它们之间的关联如下(A 连接 B，B 连接 C，A 连接 C):

      B
    /   \
   A --- C

它看起来非常简单，但是当我运行以下代码时，我得到了一个空集，即使我将搜索限制为仅通过 C 连接 B 时得到的结果也是如此:

SELECT A.* FROM A
INNER JOIN C ON C.id = A.c_id
INNER JOIN B AS B_thru_C ON B_thru_C.id = C.b_id
INNER JOIN B AS B_from_A ON B_from_A.id = A.b_id
WHERE B_thru_C.field = 'myvalue' OR B_from_A.field = 'myvalue';
# yields an empty set

SELECT A.* FROM A
INNER JOIN C ON C.id = A.c_id
INNER JOIN B AS B_thru_C ON B_thru_C.id = C.b_id
WHERE B_thru_C.field = 'myvalue';
# yields results

Answer 1

这个怎么样？

SELECT A.* FROM A
LEFT OUTER JOIN C ON C.id = A.c_id
INNER JOIN B ON B.id = A.b_id OR B.id = C.b_id
WHERE B.field = 'myvalue';