Create a SQL Stored Procedure with Dynamic Column Names - sql-server

Question

I have the following stored procedure:
ALTER PROCEDURE [dbo].[sp_RequestCategoryCount]
#StDate1 DATE,
#EnDate1 DATE,
#StDate2 DATE,
#EnDate2 DATE
AS
BEGIN
SELECT DISTINCT RQ.request_category
INTO #ReqCat
FROM
(SELECT DISTINCT request_category
FROM [VerInt_OneViewServiceReq]
UNION ALL
SELECT DISTINCT request_category
FROM [VerInt_OneViewServiceReq2]) RQ
SELECT
'1' as Iteration,
request_category,
SUM(1) AS Record_Count
INTO
#Iter1
FROM
[VerInt_OneViewServiceReq]
WHERE
request_created_dt BETWEEN #StDate1 AND #EnDate1
GROUP BY
request_category
-- UNION ALL
SELECT
'2' as Iteration,
request_category,
SUM(1) as Record_Count
INTO
#Iter2
FROM
[VerInt_OneViewServiceReq2]
WHERE
request_created_dt BETWEEN #StDate2 AND #EnDate2
GROUP BY
request_category
-- ORDER BY Iteration, request_category ASC
SELECT
RC.request_category,
IT1.Record_Count as RecordCountDateRange1,
IT2.Record_Count as RecordCountDateRange2
FROM
#ReqCat RC
LEFT JOIN
#Iter1 IT1 ON IT1.request_category = RC.request_category
LEFT JOIN
#Iter2 IT2 ON IT2.request_category = RC.request_category
DROP TABLE #ReqCat
DROP TABLE #Iter1
DROP TABLE #Iter2
END
All it does is basically compare 2 timespans of data in 2 tables by lining them up side-by-side, and works fine.
What I'd like to do is replace this from the last SELECT statement:
SELECT
RC.request_category,
IT1.Record_Count as RecordCountDateRange1,
IT2.Record_Count as RecordCountDateRange2
FROM
#ReqCat RC
with something that would "air code" like this:
SELECT
RC.request_category,
IT1.Record_Count AS "#StDate1_to_#EnDate1",
IT2.Record_Count AS "#StDate2_to_#EnDate2"
FROM
#ReqCat RC
so that the field names would indicate the dates used in the comparison.
Is this possible to do without re-writing the whole procedure, and, if so, how would I do it?

Answer 1

Yes, this is possible by using dynamic SQL. I cannot test it but more or less it should work as you specified. It will show on screen (messages area) the sentence being run and you can adjust the SELECT #SQL = ... as per your convenience until you find your correct statement:
ALTER procedure [dbo].[sp_RequestCategoryCount]
#StDate1 date,
#EnDate1 date,
#StDate2 date,
#EnDate2 date
AS
BEGIN
DECLARE #SQL AS NVARCHAR(MAX);
SELECT distinct RQ.request_category
into #ReqCat
FROM ( Select distinct request_category from [VerInt_OneViewServiceReq]
UNION ALL
Select distinct request_category from [VerInt_OneViewServiceReq2]
) RQ
Select
'1' as Iteration,
request_category,
Sum(1) as Record_Count
INTO #Iter1
from [VerInt_OneViewServiceReq]
where request_created_dt between #StDate1 and #EnDate1
group by request_category
--UNION ALL
Select
'2' as Iteration,
request_category,
Sum(1) as Record_Count
INTO #Iter2
from [VerInt_OneViewServiceReq2]
where request_created_dt between #StDate2 and #EnDate2
group by request_category
--order by Iteration, request_category ASC
SELECT #SQL = '
Select RC.request_category,
IT1.Record_Count as ['+CONVERT(VARCHAR(10), #StDate1)+'_to_'+CONVERT(VARCHAR(10), #EnDate1)+'],
IT2.Record_Count as ['+CONVERT(VARCHAR(10), #StDate2)+'_to_'+CONVERT(VARCHAR(10), #EnDate2)+']
from #ReqCat RC
LEFT JOIN #Iter1 IT1
ON IT1.request_category = RC.request_category
LEFT JOIN #Iter2 IT2
ON IT2.request_category = RC.request_category'
-- Debug purposes
PRINT #SQL;
EXEC sp_ExecuteSQL #SQL;
Drop Table #ReqCat
Drop Table #Iter1
Drop Table #Iter2
END