#1066 - 不唯一的表/别名：'clients'

Question

我有问题：

#1066 - 不唯一的表/别名：'clients'

SELECT request.*, 
       clients.ClientName AS ToClient, 
       clients.ClientName AS FromClient, 
       drivers.DriName, requesttype.ReqTName 
FROM request
    INNER JOIN clients ON clients.ClientID = request.ReqToClient
    INNER JOIN clients ON clients.ClientID = request.ReqFromClient
    INNER JOIN drivers ON drivers.DriID = request.DriID
    INNER JOIN requesttype ON requesttype.ReqTID = request.ReqTID

Answer 1

您clients在同一FROM个子句中加入了两次，这会引发错误。

表的两个化身需要有不同的别名（选择：cl_to和cl_from）：

SELECT request.*, 
       cl_to  .ClientName AS ToClient, 
       cl_from.ClientName AS FromClient, 
       drivers.DriName, requesttype.ReqTName 
FROM request
    INNER JOIN clients AS cl_to    -- alias 1 
        ON cl_to.ClientID = request.ReqToClient
    INNER JOIN clients AS cl_from   -- alias 2
        ON cl_from.ClientID = request.ReqFromClient
    INNER JOIN drivers
        ON drivers.DriID = request.DriID
    INNER JOIN requesttype
        ON requesttype.ReqTID = request.ReqTID ;

我更喜欢对所有表使用（短）别名：

SELECT rq.*, 
       cl_to  .ClientName AS ToClient, 
       cl_from.ClientName AS FromClient, 
       dr.DriName, rt.ReqTName 
FROM request AS rq
    INNER JOIN clients AS cl_to   ON cl_to.ClientID = rq.ReqToClient
    INNER JOIN clients AS cl_from ON cl_from.ClientID = rq.ReqFromClient
    INNER JOIN drivers AS dr      ON dr.DriID = rq.DriID
    INNER JOIN requesttype AS rt  ON rt.ReqTID = rq.ReqTID ;