The CASE expression is a really powerful tool that can you use to solve your SQL Server query problems. You're probably familiar with its use in mimicking if/else processing when issuing SELECT statements. However, its use is not confined strictly to this kind of processing.
Among the ways I've leveraged the CASE expression in my code:
To eliminate a cursor loop when updating rows
To perform specialized processing when using aggregate functions
To create dynamic ORDER BY and WHERE clauses without using dynamic SQL
Ex:
UPDATE dbo.Customer
SET stateDescription = CASE WHEN statecode = 'MA' THEN 'Massachusetts'
WHEN statecode = 'VA' THEN 'Virginia'
WHEN statecode = 'PA' THEN 'Pennsylvania'
ELSE NULL
END
CREATE PROCEDURE dbo.getCustomerData @sortby VARCHAR(9), @sortdirection CHAR(4)
AS
SET nocount ON
SELECT customerid, firstname, lastname, statecode, statedescription, totalsales
FROM dbo.Customer
ORDER BY
CASE @sortdirection
WHEN 'asc' THEN
CASE @sortby
WHEN 'firstname' THEN firstname
WHEN 'lastname' THEN lastname
END
END
ASC,
CASE @sortdirection
WHEN 'desc' THEN
CASE @sortby
WHEN 'firstname' THEN firstname
WHEN 'lastname' THEN lastname
END
END
DESC
GO
