How to avoid repetitive CASE statements in SQL WHILE loop doing INSERT - sql

Question

Is there a way to simplify this script so that the CASE statements are not duplicated? It can look acceptable in this shortened example but in reality the CASE statement is much longer as I have cases for "every 2 weeks, "every 4 weeks", "monthly", etc. I am using SQL Server and a WHILE statement for performance reason. Would a CTE or MERGE help?
DECLARE #theStartDate DATE
DECLARE #Interval INT
DECLARE #eventCharges TABLE
(
[EventDate] [datetime],
Person_Id int
)
SET #today = GETDATE()
SET #Interval = 0
-- delete event charges from previous user
DELETE FROM #eventCharges
-- Insert the calculated transactions
WHILE #Interval < 100
BEGIN
SET #Interval = #Interval + 1
INSERT INTO #eventCharges
SELECT
CASE
WHEN pcc.Recurrence = 'Daily'
THEN DATEADD(DAY, #Interval, #theStartDate)
WHEN pcc.Recurrence = 'Weekly'
THEN DATEADD(WEEK, #Interval, #theStartDate)
END AS EventDate
,pcc.Person_Id
FROM #personChargeCurrent pcc
WHERE CASE
WHEN pcc.Recurrence = 'Daily'
THEN DATEADD(DAY, #Interval, #theStartDate)
WHEN pcc.Recurrence = 'Weekly'
THEN DATEADD(WEEK, #Interval, #theStartDate)
END <= #today
AND NOT EXISTS(SELECT 1 FROM dbo.PersonChargeTransaction pct
WHERE pct.Person_Id = pcc.Person_Id
AND pct.PersonCharge_Id = pcc.Id
AND pct.TransactionDate =
CASE
WHEN pcc.Recurrence = 'Daily'
THEN DATEADD(DAY, #Interval, #theStartDate)
WHEN pcc.Recurrence = 'Weekly'
THEN DATEADD(WEEK, #Interval, #theStartDate)
END)
ORDER BY StartDate
END

Answer 1

You can wrap this in a function:
Create Function dbo.IntervalEnd(
#recurrence varchar(10),
#interval int,
#startDate date -- or whatever data type you're using for dates
) returns date as
begin
return case
when #recurrence = 'Daily' then dateadd(day, #interval, #startDate)
when #recurrence = 'Weekly' then dateadd(week, #interval, #startDate)
end
end
Then
Insert Into #eventCharges
Select
dbo.IntervalEnd(pcc.Recurrence, #Interval, #theStartDate) as EventDate,
pcc.Person_Id
From
#personChargeCurrent pcc
Where
dbo.IntervalEnd(pcc.Recurrence, #Interval, #theStartDate) <= #today And
Not Exists (
Select
1
From
dbo.PersonChargeTransaction pct
Where
pct.Person_Id = pcc.Person_Id And
pct.PersonCharge_Id = pcc.Id And
pct.TransactionDate
= dbo.IntervalEnd(pcc.Recurrence, #Interval, #theStartDate)
)
There are overheads for using a function. You'll have to decide if the slightly reduced performance is worth the tradeoff for increased readibility.

Answer 2

Yes, a CTE should help. Try changing your INSERT statement to:
WITH cte as
(SELECT CASE
WHEN Recurrence = 'Daily'
THEN DATEADD(DAY, #Interval, #theStartDate)
WHEN Recurrence = 'Weekly'
THEN DATEADD(WEEK, #Interval, #theStartDate)
END AS EventDate,
p.*
FROM #personChargeCurrent p)
INSERT INTO #eventCharges
SELECT cte.EventDate, cte.Person_Id
FROM cte
WHERE cte.EventDate <= #today AND
NOT EXISTS
(SELECT 1
FROM dbo.PersonChargeTransaction pct
WHERE pct.Person_Id = cte.Person_Id AND
pct.PersonCharge_Id = cte.Id AND
pct.TransactionDate = cte.EventDate)
ORDER BY StartDate

Answer 3

You could create a temporary table in which to insert the calculated fields and then use that table with a join to insert the data / apply the conditions