Dynamically setting Where condition in query - sql

Question

I am looking for a method where I need to have conditions on my WHERE clause change dynamically based on the data.
Please find the mock data for my scenario.
-----------------------------------
ConditionID ConditionName
-----------------------------------
1 N/A
2 Over
3 Under
--------------------------------------------------------------
ID Amount ThresholdAmount ConditionID
--------------------------------------------------------------
1 90 100 3
2 190 100 2
3 90 100 2
4 190 100 3
5 90 100 1
I need to compare the [Amount] against the [ThresholdAmount] based on the [ConditionID]. For example if the condition is 'Over' then the [Amount] should be over the [ThresholdAmount] and if not satisfied then the record should be filtered out.
NOTE: I am just looking if there is any better approach than mine.
My Approach:
WHERE
1 = CASE
WHEN ConditionName = 'OVER' THEN
CASE WHEN ([Amount] >= [ThresholdAmount]) THEN 1 ELSE 0 END
WHEN ConditionName = 'UNDER' THEN
CASE WHEN ([Amount] <= [ThresholdAmount]) THEN 1 ELSE 0 END
WHEN ConditionName = 'N/A' THEN
1
END
Thanks,
Prakazz

Answer 1

I think you are using the word "Dynamically" wrong here, what you mean is not really dynamic. Search for dynamic sql to get a feel for the difference.
It's usually best to avoid case expressions in the where clause. Your where clause can be rewritten as:
WHERE (ConditionName = 'OVER' AND [Amount] >= [ThresholdAmount])
OR (ConditionName = 'UNDER' AND [Amount] <= [ThresholdAmount])
OR ConditionName = 'N/A'
By the way, you mention "if the condition is 'Over' then the [Amount] should be over the [ThresholdAmount]", but in your code you check whether Amount is 'over' or equal to ThresholdAmount. I followed what your code does.
I also extended your assumption that the database is case-insensitive.