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

我问：可能合并结果吗？

我希望结果有点像这样：

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order by。由于您的示例查询没有order by，因此两者是等效的。

但更一般地说，您似乎想要交错值。您可以使用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;

Answer 2

只需订购统一的结果。

SELECT *
FROM (
    SELECT Column1, Column2 FROM tableA
    UNION ALL 
    SELECT Column1, Column2 FROM tableB
) Results 
ORDER BY Column1, Column2

合并结果联合所有sql

我问：可能合并结果吗？

2 个答案: