如何根据另一个查询向现有查询结果添加 2 列？

Question

I have a query like this:

SELECT 
   field1 as field1 , 
   field2 as field2 , 
   (select count(*) from ... where ...=field1) as field3
FROM
 ...

And it works fine - and I see 3 columns in results

The I need to add one more column for internal query:

SELECT 
       field1 as field1 , 
       field2 as field2 , 
       (select count(*) as my_count, sum(*) as my _sum from ...where ...=field1 ) as field3
    FROM
     ...

this syntax doesn't work.

How can I achieve it?

Answer 1

This partial query makes it unsure what you really want, but I would expect that the subquery actually correlates to the outer query (otherwise, you could just cross join ). If so, a typical solution is a lateral join.

In Postgres:

select 
   field1 as field1, 
   field2 as field2, 
   x.*
from ...
left join lateral (
     select count(*) as my_count, sum(*) as my _sum from ... 
) x

Oracle supports lateral joins starting version 12. You just need to replace left join lateral with outer apply .

Answer 2

The following would seem to do what you want, and it should work fine in Oracle 9i:

SELECT t.field1, 
       t.field2,
       x.my_count,
       x.my_sum
  FROM SOME_TABLE t
  LEFT OUTER JOIN (select FIELD1,
                          count(*) as my_count,
                          sum(SOME_FIELD) as my_sum
                     from SOME_OTHER_TABLE
                     GROUP BY FIELD1) x
    ON x.FIELD1 = t.FIELD1

Answer 3

You can use a CTE (Common Table Expression) to precompute the values:

WITH
q as (select count(*) as my_count, sum(*) as my _sum from ... )
SELECT 
       field1 as field1 , 
       field2 as field2 , 
       q.my_count as field3, 
       q.my_sum as field4
FROM
...
CROSS JOIN q

Or... you can always use the less performant, simpler way:

SELECT 
       field1 as field1 , 
       field2 as field2 , 
       (select count(*) from ... ) as field3,
       (select sum(*) from ... ) as field4
    FROM
     ...

Answer 4

With your limited (& a bit confusing - 2 databases, sum(*)...) info,

here is the logic:

SELECT 
       field1 as field1 , 
       field2 as field2 , 
       (select count(*) from ... ) as my_count,
       (Select sum(<my field>) from ...) as my _sum 
    FROM
     ...