MySQL:结合2个JOINS

Question

结合2个JOINS有问题.以下两个陈述都有效.我还在2个DB中包含了相关字段.我的问题是:1)如何将2个陈述合并为1个陈述？2)如何引用我的php中的行来区分结果是来自mmpreID JOIN还是mmparID JOIN？

谢谢

DB: matchmaker
mmpreID
mmparID

DB: users
uID
ufname
ulname

SELECT matchmaker.mmpreID, matchmaker.mmparID, users.uID, users.ufname, users.ulname 
FROM matchmaker 
LEFT JOIN users ON matchmaker.mmparID = users.uID

SELECT matchmaker.mmpreID, matchmaker.mmparID, users.uID, users.ufname, users.ulname 
FROM matchmaker 
LEFT JOIN users ON matchmaker.mmpreID = users.uID

Answer 1

SELECT m.mmpreID, m.mmparID, u.uID, u.ufname, u.ulname,
    case 
        when m.mmparID = u.uID then 'mmparID'
        when m.mmpreID = u.uID then 'mmpreID'
        else null 
    end as Source
FROM matchmaker m
LEFT JOIN users u ON m.mmparID = u.uID or m.mmpreID = u.uID 

更新:

SELECT m.mmpreID, m.mmparID,
    upar.uID as upar_UID, 
    upar.ufname as upar_UFNAME, 
    upar.ulname as upar_ULNAME,
    upre.uID as upre_UID, 
    upre.ufname as upre_UFNAME, 
    upre.ulname as upre_ULNAME
FROM matchmaker m
LEFT JOIN users upar ON m.mmparID = upar.uID 
LEFT JOIN users upre ON m.mmpreID = upre.uID