MYSQL:左键使用同一字段连接同一个表两次
我有一个存储管理员和普通客户的用户表:MYSQL:左键使用同一字段连接同一个表两次,mysql,left-join,self-join,Mysql,Left Join,Self Join,我有一个存储管理员和普通客户的用户表: ID Name Role 1 John Admin 2 Sara User 3 Pete User 4 Nick User 另一个存储请求的表: ID Updatedby Createdby DateCreated DateUpdated 1 1 2 10/12/2017 21/01/2018 2 1 1
ID Name Role
1 John Admin
2 Sara User
3 Pete User
4 Nick User
另一个存储请求的表:
ID Updatedby Createdby DateCreated DateUpdated
1 1 2 10/12/2017 21/01/2018
2 1 1 11/12/2017 22/01/2018
3 1 3 12/12/2017 23/01/2018
4 2 2 13/12/2017 24/01/2018
我正在尝试创建一个如下所示的视图:
ID Updatedby Createdby DateCreated DateUpdated
1 John Sara 10/12/2017 21/01/2018
2 John John 11/12/2017 22/01/2018
3 John Pete 12/12/2017 23/01/2018
4 Sara Sara 13/12/2017 24/01/2018
创建查询时面临的问题是,我尝试两次左连接到用户表。如何指定Users.Name是Updatedby还是Createdby?这就是我的意思:
SELECT
request.ID,
users.Name, /*name for Createdby */
users.Name, /*name for Updatedby */
requests.DateCreated,
requests.DateUpdated
FROM
requests
LEFT JOIN
users ON requests.Updatedby = users.ID
我无法理解这个逻辑。这是一个例子:
SELECT toD.dom_url AS ToURL,
fromD.dom_url AS FromUrl,
rvw.*
FROM reviews AS rvw
LEFT JOIN domain AS toD
ON toD.Dom_ID = rvw.rev_dom_for
LEFT JOIN domain AS fromD
ON fromD.Dom_ID = rvw.rev_dom_from
您可以使用您可以加入它两次并给它不同的别名join X as x1 on…,X as X2 on…,您可以尝试users。Name as Createdby,users。Name as updatedby是否确实要左加入而不是内部加入?你真的能拥有一个与用户不匹配的CreatedBy吗?嗨。只需通过谷歌搜索标题或阅读SQLJoin的介绍,了解它的功能告诉您如何做到这一点。请看&。PS这是一个。