Conditional T-SQL using CASE WHEN

Let's say you need to retrieve data from one table and whether or not each record contains data in the second table, and instead of data from the second table you want to display "yes" or "No". Your best bet is to use CASE WHEN in your SELECT:

SELECT DISTINCT c.CustomerID as [Customer ID], c.CompanyName as [Company Name], 
CAST(CASE WHEN o.CustomerID IS NULL THEN 'No' ELSE 'Yes' END as varchar) as [Has Orders]  
FROM Customers as c 
LEFT JOIN Orders as o ON c.CustomerID=o.CustomerID

The resulting data would look like this:

Customer ID	Company Name	Has Orders
OCEAN	Océano Atlántico Ltda.	Yes
OLDWO	Old World Delicatessen	Yes
OTTIK	Ottilies Käseladen	Yes
PARIS	Paris spécialités	No
PERIC	Pericles Comidas clásicas	Yes