mysql - MySQL 中的条件内连接语句

Question

有没有一种方法可以根据另一个表中字段的值有条件地更改我内部加入的表？这是我到目前为止(但它出错)的结果:

SELECT 
    j.jobID, j.jobNumber,
    CASE
        WHEN j.idType = 'dealership' THEN d.dealershipName
        WHEN j.idType = 'Group' THEN g.groupName
        WHEN j.idType = 'Agency' then a.agencyName
    END as dealershipName,
    CASE
        WHEN p.manualTimestamp != '0000-00-00 00:00:00' THEN UNIX_TIMESTAMP(p.manualTimestamp)
        WHEN p.manualTimestamp = '0000-00-00 00:00:00' THEN p.timestamp
    END as checkTS,
    CONCAT_WS(' ', ui.fName, ui.lName) as salesRep
FROM jobs j
LEFT JOIN dealerships d ON j.dealershipID = d.dealershipID
LEFT JOIN dealershipgroups g ON j.dealershipID = g.groupID
LEFT JOIN agencies a ON j.dealershipID = a.agencyID
INNER JOIN payments p ON j.jobID = p.jobID
IF j.idType = 'dealership' THEN 
    INNER JOIN smdealershipjoins smdj ON j.dealershipID = smdj.dealership
    INNER JOIN userinfo ui ON smdj.sm = ui.userID           
ELSEIF j.idType = 'Group' THEN 
    INNER JOIN smgroupjoins gj ON j.dealershipID = gj.groupID
    INNER JOIN userinfo ui ON gj.sm = ui.userID
ELSEIF j.idType = 'Agency' THEN 
    INNER JOIN smagencyjoins aj ON j.dealershipID = aj.agencyID
    INNER JOIN userinfo ui on aj.sm = ui.userID
END IF

因此，有一个表 (jobs)，其中包含 idType(经销商、集团或代理)和一个 clientID(称为 dealershipID)。我需要做的是加入某个表(基于 idType)以确定哪个销售经理“拥有”客户帐户。如果 idType = 'dealership' 我需要加入 smdealershipjoins，如果它是 'Group' 我需要加入 smgroupjoins，如果它是 'agency' 我需要加入 smagencyjoins 这样我就可以将该表加入 userinfo 以获得销售经理的名字。

我也尝试过使用 case 语句来进行内部连接，但这也报错了。

Answer 1

左/外连接到三个选项中的每一个，您选择的条件将处理其余部分。

也许是这样的:

...
LEFT JOIN smdealershipjoins smdj 
    ON j.dealershipID = smdj.dealership
LEFT JOIN smgroupjoins gj 
    ON j.dealershipID = gj.groupID
LEFT JOIN smagencyjoins aj 
    ON j.dealershipID = aj.agencyID
LEFT JOIN userinfo ui 
    ON ui.userID = CASE
        WHEN j.idType = 'dealership' THEN smdj.sm
        WHEN j.idType = 'Group' THEN gj.sm
        WHEN j.idType = 'Agency' then aj.sm
    END