How to Implement a Conditional WHERE Clause Based on a Parameter in SQL Server?

Conditional WHERE clause in SQL Server

Question:

How to create a conditional WHERE clause in SQL Server, especially where the condition changes based on parameter values?

Answer:

To create a conditional WHERE clause, you can use an expression in the WHERE clause that evaluates to TRUE for records that satisfy the condition and to FALSE for records that do not. Consider the following query:

<code class="language-sql">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)
    )</code>

In this query, the WHERE clause contains the following conditions:

<code class="language-sql">(ISNULL(@JobsOnHold, 0) = 1 AND DateAppr >= 0) 
OR 
(ISNULL(@JobsOnHold, 0) != 1 AND DateAppr != 0)</code>

This conditional expression evaluates to TRUE for records that satisfy:

• If @JobsOnHold equals 1, then DateAppr must be greater than or equal to 0.
• If @JobsOnHold is not equal to 1, then DateAppr must not be equal to 0.

By using this conditional expression, you can dynamically apply different conditions to the query based on the value of the @JobsOnHold parameter. This allows for greater flexibility and control when filtering data.

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