lets say I have a huge select on a certain table. One value for a column is calculated with complex logc and its called ColumnA. Now, for another column, I need the val
If you want to reference a value that's computed in the SELECT
clause, you need to move the existing query into a sub-SELECT:
SELECT
/* Other columns */,
ColumnA,
ColumnA + 10 as ColumnB
FROM
(select table.id, table.number, complex stuff [ColumnA].. from table ...
) t
You have to introduce an alias for this table (in the above, t
, after the closing bracket) even if you're not going to use it.
(Equivalently - assuming you're using SQL Server 2005 or later - you can move your existing query into a CTE):
;WITH PartialResults as (
select table.id, table.number, complex stuff [ColumnA].. from table ...
)
SELECT /* other columns */, ColumnA, ColumnA+10 as ColumnB from PartialResults
CTEs tend to look cleaner if you've got multiple levels of partial computations being done, I.e. if you've now got a calculation that depends on ColumnB to include in your query.