How Can I Use a CASE Statement to Filter Data Dynamically in a SQL WHERE Clause?

CASE statement in SQL WHERE clause

In SQL, the CASE statement provides a conditional evaluation mechanism. It allows you to specify different conditions and return corresponding numerical values ​​based on these conditions. This is especially useful in WHERE clauses to filter data based on different conditions.

Assume the following scenario: You need to retrieve data from a view named "viewWhatever" based on the values ​​of the location type parameter "@locationType" and the location ID parameter "@locationID". The location type can be 'location', 'area' or 'division'.

Use CASE statement

To achieve this functionality using a CASE statement in the WHERE clause, you can build the query as follows:

<code class="language-sql">SELECT column1, column2
FROM viewWhatever
WHERE
@locationID = 
  CASE @locationType
      WHEN 'location' THEN account_location
      WHEN 'area' THEN xxx_location_area 
      WHEN 'division' THEN xxx_location_division 
  END</code>

Description

• The CASE statement is placed after the WHERE keyword.
• It evaluates the value of "@locationType" as a condition variable.
• For each WHEN clause, specify the columns to check for equality with "@locationID" based on the location type.
• END keyword terminates the CASE statement.

Avoid redundant equals operators

Please note that in the example provided, the "=@locationID" part at the end of each WHEN clause is incorrect. The CASE statement itself assigns the correct column to compare with "@locationID".

Dynamic SQL

If your location type and column names are not known when you write the query, you can build a CASE statement on the fly using a stored procedure or dynamic SQL.

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