Question

我有两个查询（示例版本） -

查询A：

select 
  col1 as COL1,
  col2 as COL2,
  sum(col3) as COL3
from table1 join table11 ..
group by col1, col2;

查询B：

select 
  col1 as COL1,
  col2 as COL2,
  count(col3) as COL3
from table2
group by col1, col2;

我想加入他们两个并输出如下所示。试过这个

select A.COL1, A.COL2, greatest(A.COL3, B.COL3)
from (query A) A
UNION (query B) B

但收到错误

SQL0104N An unexpected token "END-OF-STATEMENT" was found following "col2) B". Expected tokens may include: "JOIN <joined_table>". SQLSTATE=42601

两个查询单独运行正常，但如果像上面那样使用UNION进行组合，则会出错。

有没有更好的方法来实现这一目标？

Answer 1

看起来您需要加入，而不是联盟：

select A.COL1, A.COL2, greatest(A.COL3, B.COL3)
from (query A) A
join (query B) B on A.COL1 = B.COL1 and A.COL2 = B.COL2

根据您的需要，您可能需要left join，right join或full outer join而不是内部join。

Answer 2

 with A as  
 (
 select 
 col1 as COL1,
 col2 as COL2,
 sum(col3) as COL3
 from table1 join table11 ..
 group by col1, col2
 ),
 B as
 (
 select 
 col1 as COL1,
 col2 as COL2,
 count(col3) as COL3
 from table2
 group by col1, col2
 ) 

 select ifnull(A.COL1, B.COL1) as COL1, ifnull(A.COL2, B.COL2) as COL2,
 greatest(ifnull(A.COL3, 0), ifnull(B.COL3, 0)) as great
 from A full outer join B on A.COL1 = B.COL1 and A.COL2 = B.COL2

DB2 SQL：组合两个查询并选择最多一个聚合列

2 个答案: