mysql并排组合查询结果

Question

简单的问题，我不能把我的头。我只想将没有公共数据的两个表并排组合。

table1    table2   ->   result 
a  b       e  f          a  b  e  f
c  d       g  h          c  d  g  h
           i  j          \n \n i  j

Answer 1

您可以使用RIGHT JOIN完成此操作，并使用ROW_NUMBER为每个表分配一个id。请参见下面的查询：

 SELECT A.column1,A.column2,B.column1,B.column2 FROM
    (SELECT
         @row_number1:=@row_number1+1 AS RowNumber1,
         column1,
         column2
    FROM Table1, (SELECT @row_number1:=0)AS x ORDER BY column1) AS A
    RIGHT JOIN
    (SELECT
         @row_number2:=@row_number2+1 AS RowNumber2,
         column1,
         column2
    FROM Table2, (SELECT @row_number2:=0)AS y ORDER BY column1) AS B
    ON A.RowNumber1=B.RowNumber2

Answer 2

SQL表本身是无序的，因此需要一个排序行的键。您可以使用变量创建一个。

您的表有不同的行数。这意味着full outer join是可取的，但这在MySQL中是不可用的。因此，您可以使用聚合和union all来做您想做的事情。

select max(col1) as col1, max(col2) as col2, max(col3) as col3, max(col4) as col4
from ((select col1, col2, null as col3, null as col4, @rn1 := @rn1 + 1 as rn
       from table1 cross join (select @rn1 := 0) vars
      ) union all
      (select null, null, col3, col4, @rn2 := @rn2 + 1 as rn
       from table2 cross join (select @rn2 := 0) vars
      )
     ) tt
group by rn