Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

A Simple CASE
A simple CASE takes an expression that equates to a Boolean result. Let’s get right to an example:
Use AdventureWorks2008;
GO
SELECT TOP 10 SalesOrderID,
SalesOrderID % 10 AS ‘Last Digit’,
Position = CASE SalesOrderID % 10
WHEN 1 THEN ‘First’
WHEN 2 THEN ‘Second’
WHEN 3 THEN ‘Third’
WHEN 4 THEN ‘Fourth’
ELSE ‘Something Else’
END
FROM Sales.SalesOrderHeader;
For those of you who aren’t familiar with it, the % operator is for a modulus. A modulus works in a similar
manner to the divide by (/), but it gives you only the remainder — therefore, 16 % 4 = 0 (4 goes into 16
evenly), but 16 % 5 = 1 (16 divided by 5 has a remainder of 1). In the example, since we’re dividing by
10, using the modulus is giving us the last digit of the number we’re evaluating.
Let’s see what we got with this:
SalesOrderID Last Digit Position
------------ ----------- --------------
43793 3 Third
51522 2 Second
57418 8 Something Else
43767 7 Something Else
51493 3 Third
72773 3 Third
43736 6 Something Else
51238 8 Something Else
53237 7 Something Else
43701 1 First
(10 row(s) affected)
Notice that whenever there is a matching value in the list, the THEN clause is invoked. Since we have an
ELSE clause, any value that doesn’t match one of the previous values will be assigned whatever we’ve
put in our ELSE. If we had left the ELSE out, then any such value would be given a NULL.
Let’s go with one more example that expands on what we can use as an expression. This time, we’ll use
another column from our query:
USE AdventureWorks2008;
GO
SELECT TOP 10 SalesOrderID % 10 AS ‘OrderLastDigit’,
ProductID % 10 AS ‘ProductLastDigit’,
“How Close?” = CASE SalesOrderID % 10
WHEN ProductID % 1 THEN ‘Exact Match!’
WHEN ProductID % 1 - 1 THEN ‘Within 1’
WHEN ProductID % 1 + 1 THEN ‘Within 1’
Chapter 11: Writing Scripts and Batches
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