mysql - 合并所有 sql 中的结果

Question

表 A:

Column1 | Column2
tableA01 | tableA11
tableA02 | tableA22

表 B:

Column1 | Column2
tableB01 | tableB11
tableB02 | tableB22

当sql在这些表中使用union all时，结果如下:

SQL

SELECT * FROM tableA UNION ALL SELECT * FROM tableB

结果

Column1  | Column2
tableA01 | tableA11
tableA02 | tableA22
tableB01 | tableB11
tableB02 | tableB22

---

请问:是否可以合并结果？

我想要这样的结果:

Column1  | Column2
tableA01 | tableA11
tableB01 | tableB11
tableA02 | tableA22    
tableB02 | tableB22

谢谢!

Answer 1

您的结果集是相同的，因为结果集无序，除非您有排序方式。因为您的示例查询没有 order by，所以两者是等价的。

不过，更一般地说，您似乎想要交错这些值。您可以通过以下方式使用 order by 执行此操作:

select ab.*
from ((select a.*, (@rna := @rna + 1) as rn, 1 as which
       from a cross join (select @rna := 0) params
       order by <something>  -- You should order by something here so the ordering is well defined
      ) union all
      (select b.*, (@rnb := @rnb + 1) as rn, 2 as which
       from b cross join (select @rnb := 0) params
       order by <something>  -- You should order by something here so the ordering is well defined
      )
     ) ab
order by rn, which;