T-SQL: Select Case Example
Jack Donnell,
[email protected]
Select Case allows you to present data in various way. You can take numbers and return text values and express
certian conditions based on the value of a certain column.
Another example would be that you have a table Naughty_Nice in the Santa Database a data column Nice (INT Datatype) .
There are two distinct values in the column. The Value of 0 equals 'No' and the value 1 equals yes. You wanted to speed
stuff up and use less space by selecting a number and not use text Naughty/Nice.
Santa needs a list and he complains that 1 and 0 will not make sense to him at 30,000 feet. It's so hard to
communicate to a guy that still thinks wooden toys are a big hit. He's a bit too hands-on, and lacks the technical
skills to really understand that we want to optimize the database.
You want to query the table to find out which Child is Naughty and which is nice, but return a value that 'Ole Red' will
benefit from. So you quickly point out that a New Yankee Workshop Maraton is on and Norm is demonstrating some $200,000
combination tablesaw, sander with an auto-jig thingy. He takes off and you write the following query.
Select c.ChildName, g.Gift, l.Location, case(n.Nice) when 1 then 'Nice' Else 'Naughty' End From Child c, Gift G, Location L, Naughty_Nice n Where c.childid=g.childid and c.childid=n.childid Order by N.Nice N.nice, l.location,g.Gift, c.ChildName
---This example uses the SQL Server Example Database NorthWind ---Purpose: Define by Month and Year Total Orders for Years 1996-1998 ---Use Case Function to gather Totals by Year ---Example By Jack Donnell [email protected] USE NorthWind GO USE NorthWind GO SELECT MONTH(OrderDate) AS Month, SUM(CASE YEAR(OrderDate) WHEN 1996 THEN 1 ELSE 0 END) AS Orders1996, SUM(CASE YEAR(OrderDate) WHEN 1997 THEN 1 ELSE 0 END) AS Orders1997, SUM(CASE YEAR(OrderDate) WHEN 1998 THEN 1 ELSE 0 END) AS Orders1998 FROM Orders GROUP BY MONTH(OrderDate) ORDER BY MONTH(OrderDate) COMPUTE SUM(SUM(CASE YEAR(OrderDate) WHEN 1996 THEN 1 ELSE 0 END) ), SUM(SUM(CASE YEAR(OrderDate) WHEN 1997 THEN 1 ELSE 0 END)), sum(SUM(CASE YEAR(OrderDate) WHEN 1998 THEN 1 ELSE 0 END)) The OutPut Would be : Month Orders1996 Orders1997 Orders1998 ----------- ----------- ----------- ----------- 1 0 33 55 2 0 29 54 3 0 30 73 4 0 31 74 5 0 32 14 6 0 30 0 7 22 33 0 8 25 33 0 9 23 37 0 10 26 38 0 11 25 34 0 12 31 48 0 sum =========== 152 sum =========== 408 sum =========== 270 (13 row(s) affected)