Case statement in sql using other selected columns in the same statement - sql-server

Question

I would like to know if the following is possible in SQL server 2005. Column A and B are calculated using other case statements in my actual stored proc. I don't want to repeat the same for another field unnecessarily. If this is not syntactically possible, any other ideas?
SELECT A, B, CASE WHEN column1='1' THEN A ELSE B END Col1.
Modified version of actual query provided as requested. CTE kind of seems to be tough in this model. WANNABE is the column I want to accomplish in the sub select statement.
SELECT 1 AS Region, 'Test',
CAST(Work AS NUMERIC(18,2)) Work,
Work + 2 AS Work2,
WANNABE
FROM
(
SELECT
ROW_NUMBER() OVER(PARTITION BY G.Value, C.C, FR.Mod1 ORDER BY FR.Date DESC, FG.Date DESC, FC.Date DESC) ROW,
CASE WHEN COALESCE(FR.Mod1, '') = '' THEN '' ELSE FR.Mod1 END Mod1,
CASE WHEN #var1=1 AND #var2 = 1 THEN FR.Col1 * G.Value
WHEN #var1=1 AND #var2 = 0 THEN FP.Col1 * G.Value END Work,
CASE WHEN 1=1 THEN Work ELSE 1 END WANNABE,
(
SELECT Col3
FROM Table2
WHERE c = FR.Value
) AS Custom
FROM MainTable FR
JOIN #C C ON FR.Col2 = C.Col2
LEFT JOIN Function1(#VersionDate) cv ON cv.Code = C.Code
LEFT JOIN Function2(#VersionDate) hv ON hv.Code = C.Code
LEFT JOIN #G G ON 1 = 1
LEFT JOIN SubTable1 FG ON FG.Number = G.Value, 2 AND FG.Date = #VersionDate
LEFT JOIN SubTable2 FO ON FO.Number = G.Value
AND FO.Date = #VersionDate AND FO.Code = FR.Code AND FR.Mod1 = FO.Mod1
LEFT JOIN SubTable3 FP ON FP.Code = FR.Code AND FP.VersionDate = #Versiondate
AND CASE WHEN DATALENGTH(FR.Mod1) = 0 THEN '00' ELSE FR.Mod1 END = CASE WHEN DATALENGTH(FP.Mod1) = 0 THEN '00' ELSE FP.Mod1 END
LEFT JOIN SubTable4 FC ON FC.Date = #VersionDate
WHERE FR.Date = #VersionDate
) x
WHERE x.Row = 1
AND RTRIM(LTRIM(x.Col1)) IN ('', '2')

Answer 1

You can define the A,B column aliases in a CTE then reference them in an outer select.
;WITH CTE AS
(
SELECT CASE ... END AS A,
CASE ... END AS B,
column1
FROM your_table
)
SELECT A,
B,
CASE WHEN column1='1' THEN A ELSE B END Col1
FROM CTE
Similarly you can also define them in a CROSS APPLY that is sometimes a bit less verbose.
A silly example just to show the syntax is
SELECT A,
B,
CASE WHEN type='P' THEN A ELSE B END Col1
FROM master..spt_values
CROSS APPLY (SELECT CASE WHEN number %2 = 1 THEN 1 END,
CASE WHEN number %2 = 0 THEN 0 END) T(A,B)
Following your update you can replace the derived table with a CTE and nest CTEs as follows
;WITH x as
(
SELECT
ROW_NUMBER() OVER(PARTITION BY G.Value, C.Code, FR.Mod1 ORDER BY FR.Date DESC, FG.Date DESC, FC.Date DESC) ROW,
...<snip>
WHERE FR.Date = #VersionDate
),
x2 As
(
SELECT *,
CASE WHEN 1=1 THEN Work ELSE 1 END WANNABE
FROM x
)
SELECT 1 AS Region, 'Test',
CAST(Work AS NUMERIC(18,2)) Work,
Work + 2 AS Work2,
WANNABE
FROM x2
WHERE x2.Row = 1
AND RTRIM(LTRIM(x2.Col1)) IN ('', '2')

Answer 2

Yeah it is posible, but how is all your sql statement? You can use the case statement in the select statement as you are using it.
Something like this
SELECT SUM((CASE WHEN column1='1' THEN 10 ELSE 0 END)) AS A, SUM((CASE WHEN column1='2' THEN 10 ELSE 0 END)) AS B
FROM YourTable