同一字段的两个表之间的两个联接

Question

我在MySQL数据库V_Activity_SameTimeActivity中有一个表，其中有两个字段SameTimeActivityId和ActivityId。它们都是引用ACTIVITY_V表中的Id字段的字段。我想创建一个视图，向我显示V_Activity_SameTimeActivity表中两组ID的ACTIVITY_V.Name字段。我可以选一个，但不能选另一个。到目前为止，此查询。

SELECT
ACTIVITY_V.Name AS MasterActivity,
V_Activity_SameTimeActivity.ActivityId,
V_Activity_SameTimeActivity.SameTimeActivityId

FROM V_Activity_SameTimeActivity
INNER JOIN ACTIVITY_V ON V_Activity_SameTimeActivity.ActivityId = ACTIVITY_V.Id;

我还希望将ACTIVITY_V.Name AS SametimeActivity与V_Activity_SameTimeActivity.SameTimeActivityId一起显示在ACTIVITY_V.Id上

Answer 1

您可以ACTIVITY_V重新加入SameTimeActivityId进行映射

SELECT
    t2.Name AS MasterActivity,
    t3.Name AS SameActivityName,
    t1.ActivityId,
    t1.SameTimeActivityId
FROM V_Activity_SameTimeActivity t1
LEFT JOIN ACTIVITY_V t2 ON t1.ActivityId = t2.Id;
LEFT JOIN ACTIVITY_V t3 ON t3.ActivityId = t1.SameTimeActivityId;