I nee开发者_JAVA技巧d to generate a result set in two steps. The first step is simple and generates a base in-memory result set (let's call it B
). In the second step, I need to add an additional column to B
(let's call it c
). For each row in B
, c
can be calculated by using an aggregate function on B
based on the values of that row (this does look inefficient though).
The final result set is B + c
. Results must be sorted by a column from B
as well as the c
column, so the whole thing should be a single query.
Getting B
is simple, but how do I process it further based on its contents?
EDIT. Here's a table analogy to illustrate what I mean by "applying an aggregate function on B
based on each row in B
":
Say, we have a table T
with a column col
. Let's say that for each row in T
we want to calculate the number of rows that have a higher col
value. You could do it like this:
select
t1.*,
(select sum(case when t2.col > t1.col then 1 else 0 end) from T t2) as count
from T t1
In my case the problem is that B
is not a real table but an in-memory result set. How can I process it in a similar way?
OK - I'll give it another go.
Aliasing both the in memory results set and the columns that you need to use in that results set to derive c should work.
To continue your example from above:
select B.col,
(select sum(case when B2.col > B.col then 1 else 0 end) from (select whatever_col as col
from whatever_table) B2) as c
from
(select whatever_col as col from whatever_table) as B;
Let me know if I've got the wrong end of the stick again!
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