Question

在MySQL中，我希望SELECT A.* FROM A满足内部联接条件，无论是直接（通过表B）还是通过另一个联接表（C ），WHERE B.field = myvalue。任何人都可以指出获得结果的正确方法吗？

我有以下表格：A，B，C，它们如下关联（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，我得到一个空集，即使我在将搜索限制为仅通过C加入B时得到结果：

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';

Mysql内连接两次并在两个连接上使用WHERE

1 个答案: