The CASE statement is a very flexible tool. Here are just a few of the tricks
you can work with it.
One of the simplest things you can do is to derive a columns contents based
on it’s contents, or the contents of another data item.
You can use CUBE and ROLLUP to produce totals and subtotals within a result
set, but because SQL Server places NULLS for non-totaled columns in the total
rows, they do not always look very pretty. In this example we use the CASE
statement to place emphasis on the subtotal lines.
This batch lists of sales by store, and gives a general indication of the
stores performance against the average quantity of sales per store.
This query batch starts by calculating the average of total sales per store,
which is stored in the variable @storeAvg, then that average is used to rate the
stores sales performance.
Grouping data into ranges
This example calculates the number of orders in certain size ranges. It also
shows off the power of SQL as a set-based language: to code this as in a
procedural language like VB would not be able to do this in a single statement.
CASE statements can be used in an ‘ORDER BY clause to order non-sequential
data. This example sorts stores by name, but puts all the stores in California
at the top of the list.
SELECT stor_name, state FROM stores ORDER BY CASE state WHEN 'CA' then 1 ELSE 2 END, stor_name
This article discusses how to increase performance of complex
UPDATE statements by using CASE.
This SQL 2000 article contains a section that shows how to use the CASE
statement in a User
Defined Function to enforce complex declarative constraints