mysql并排查询结果

Question

简单的问题，我不能得到我的头。 我只想将两个没有共同数据的表并列在一起。

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

你可以做到这一点使用RIGHT JOIN并分配一个ID，每个表的使用ROW_NUMBER来。看到我的查询如下：

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表本质上是无序的，所以排序行的关键是可取的。您可以使用变量创建一个。

您的表格具有不同的行数。这意味着full outer join是可取的，但这在MySQL中不可用。所以，你可以做你想做采用聚集和union all什么：

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