在一个条件下加入两个表

Question

我有两个表，tblstudent和tbltrans，tblstudent包含idstudent和nmstudent，在tbltrans中包含idtrans，idstudent，trprice 我想合并这两个表，以便结果变为nmstudent和trprice但我希望tbltrans中不存在的idstudent也可以显示＆＃34; - ＆＃34;的内容。 请帮忙 Joining two table

Answer 1

结合左连接和合并：

select
    nmstudent,
    coalesce(trprice,'-')
from
    tblstudent
    left join tbltrans on
        tblstudent.idstudent=tblstudent.idstudent

Answer 2

SELECT nmstudent, CASE WHEN tprice IS NULL THEN "-" ELSE tprice END as tprice
FROM tblstudent LEFT JOIN tblstudent
ON tblstudent.idstudent = tbltrans.idstudent