How Can I Use SQL's CASE Statement to Perform Conditional Evaluations in SELECT Queries?

Understanding the CASE Statement in SELECT Queries

In SQL, the CASE statement allows you to perform conditional evaluations and return different results based on the specified conditions. This is especially useful when you want to categorize or classify data based on certain criteria.

Consider the following example:

SELECT xxx, yyy,
CASE
    WHEN bbb THEN 'blackberry'
    WHEN sss THEN 'samsung'
END 
FROM (
    SELECT ???? .....
)

In this example, the result would display the values of xxx and yyy along with the following:

Name	Age	Handphone
xxx1	yyy1	blackberry
xxx2	yyy2	blackberry

Syntax and Reference

For a comprehensive understanding of the CASE statement syntax and usage, refer to credible resources such as Microsoft's Transact-SQL Reference:

https://msdn.microsoft.com/en-us/library/ms181765.aspx

Example Usage

Let's consider a scenario where you want to categorize products in AdventureWorks2012 database based on their list prices:

USE AdventureWorks2012;
GO

SELECT ProductNumber, Name, 
"Price Range" = 
CASE 
    WHEN ListPrice = 0 THEN 'Mfg item - not for resale'
    WHEN ListPrice < 50 THEN 'Under '
    WHEN ListPrice >= 50 AND ListPrice < 250 THEN 'Under 0'
    WHEN ListPrice >= 250 AND ListPrice < 1000 THEN 'Under 00'
    ELSE 'Over 00'
END
FROM Production.Product
ORDER BY ProductNumber;
GO

This query will output the following result:

ProductNumber	Name	Price Range
1	Bike	Under 0
2	Chair	Under
3	Table	Under 0

Additional Resource

For further exploration of SQL Server, consult the SQL Server Central website:

https://www.sqlservercentral.com/

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