How Can I Implement a Conditional WHERE Clause in SQL Server to Filter Data Based on a Parameter?

Conditional WHERE clause in SQL Server

In SQL Server, the conditional WHERE clause allows you to specify different filter conditions based on specific conditions. This is useful when you need to include or exclude data from query results based on the value of a parameter or variable.

Consider the following scenario:

You wish to retrieve data from a table named [MM] based on the following criteria:

• If the @JobsOnHold parameter is set to 1, records with a DateAppr column greater than or equal to 0 are included.
• If the @JobsOnHold parameter is not set to 1, include records where the DateAppr column is not equal to 0.

The CASE statement you originally tried to use does not work in this case. Instead, you can use the following conditional WHERE clause:

SELECT 
    DateAppr,
    TimeAppr,
    TAT,
    LaserLTR,
    Permit,
    LtrPrinter,
    JobName,
    JobNumber,
    JobDesc,
    ActQty,
    (ActQty-LtrPrinted) AS L,
    (ActQty-QtyInserted) AS M,
    ((ActQty-LtrPrinted)-(ActQty-QtyInserted)) AS N
FROM 
    [test].[dbo].[MM]
WHERE 
    DateDropped = 0
    AND (
    (ISNULL(@JobsOnHold, 0) = 1 AND DateAppr >= 0) 
    OR 
    (ISNULL(@JobsOnHold, 0) != 1 AND DateAppr != 0)
    )

In this code:

• ISNULL function checks whether the @JobsOnHold parameter is empty. If empty, its value is set to 0 (default).
• The conditional expression within the AND operator applies the filter based on the value of the @JobsOnHold parameter.

By using conditional WHERE clauses, you can write more flexible and dynamic SQL queries without having to use dynamic SQL or workarounds involving if-else statements. For more information about conditional WHERE clauses, see the documentation linked in the provided answer.

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