mysql - SQL 查询 : get data from multiple table with joining each other with common field but no guarantee any table have data for sure.

Question

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Answer 1

您想要的是全外连接，而 MySQL 不支持。我建议使用 union all 和 group by 来解决这个问题:

select commonId,
       max(aName) as aName, max(bName) as bName, max(cName) as cName)
from ((select commonId, aName, NULL as bName, NULL as cName
       from tableA
      ) union all
      (select commonId, NULL as aName, bName, NULL as cName
       from tableB
      ) union all
      (select commonId, NULL as aName, NULL as bName, cName
       from tableC
      )
     ) abc
group by CommonId;

这假设您在表格中没有任何重复项。如果可能的话，您需要解释在这种情况下结果会是什么样子。