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

Chapter 11: Writing Scripts and Batches
ELSE ‘More Than One Apart’
END
FROM Sales.SalesOrderDetail
ORDER BY SalesOrderID DESC;
Notice that we’ve used equations at every step of the way on this one, yet it still works. . . .
OrderLastDigit ProductLastDigit How Close?
-------------- ---------------- -------------------
3 2 More Than One Apart
3 9 More Than One Apart
3 8 More Than One Apart
2 2 More Than One Apart
2 8 More Than One Apart
1 7 Within 1
1 0 Within 1
1 1 Within 1
0 2 Exact Match!
0 4 Exact Match!
(10 row(s) affected)
As long as the expression evaluates to a specific value that is of compatible type to the input expression,
it can be analyzed, and the proper THEN clause applied.
A Searched CASE
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This one works pretty much the same as a simple CASE, with only two slight twists:
❑ There is no input expression (remember that’s the part between the CASE and the first WHEN).
❑ The WHEN expression must evaluate to a Boolean value (whereas in the simple CASE examples
we’ve just looked at, we used values such as 1, 3, and ProductID + 1).
Perhaps what I find the coolest about this kind of CASE is that we can completely change around what is
forming the basis of our expression — mixing and matching column expressions, depending on our different
possible situations.
As usual, I find the best way to get across how this works is via an example:
SELECT TOP 10 SalesOrderID % 10 AS ‘OrderLastDigit’,
ProductID % 10 AS ‘ProductLastDigit’,
“How Close?” = CASE
WHEN (SalesOrderID % 10) < 3 THEN ‘Ends With Less Than Three’
WHEN ProductID = 6 THEN ‘ProductID is 6’
WHEN ABS(SalesOrderID % 10 - ProductID)