MySQL将多个列与左连接匹配为一个

Question

我有两张像这样的表

name  | fNatId | mNatId
=======================
Smith |      1 |      1
Doe   |      1 |      0
Owen  |      0 |      2

和这一个

id | countryName
================
 0 | U.S.
 1 | U.K.
 2 | Canada

我想把第一张表翻译成这个

Name    | Father's Nationality | Mother's Nationality
=====================================================
Smith   | U.K.                 | U.K.
Doe     | U.K.                 | U.S.
Owen    | U.S.                 | Canada

我该怎么做？使用两次LEFT JOIN投掷Not unique table/alias错误。只使用一个将两列匹配为父亲或母亲。

Answer 1

您需要为表使用唯一的别名。将您的第一个表格视为users，将第二个表格视为countries，您是否尝试过这种方式？以下应该与您正在寻找的工作完全一致。

SELECT u.name as Name, c1.countryName as FathersNationality, c2.countryName as MothersNationality

FROM users as u

LEFT JOIN countries as c1 ON c1.id = u.fNatId

LEFT JOIN countries as c2 ON c2.id = u.mNatId