I think these could be helpful for you .
Using a SELECT statement with a simple CASE expression
Within a SELECT statement, a simple CASE expression allows for only an equality check; no other comparisons are made. The following example uses the CASE expression to change the display of product line categories to make them more understandable.
SELECT ProductNumber, Category =
WHEN 'R' THEN 'Road'
WHEN 'M' THEN 'Mountain'
WHEN 'T' THEN 'Touring'
WHEN 'S' THEN 'Other sale items'
ELSE 'Not for sale'
ORDER BY ProductNumber;
Using a SELECT statement with a searched CASE expression
Within a SELECT statement, the searched CASE expression allows for values to be replaced in the result set based on comparison values. The following example displays the list price as a text comment based on the price range for a product.
SELECT ProductNumber, Name, "Price Range" =
WHEN ListPrice = 0 THEN 'Mfg item - not for resale'
WHEN ListPrice < 50 THEN 'Under $50'
WHEN ListPrice >= 50 and ListPrice < 250 THEN 'Under $250'
WHEN ListPrice >= 250 and ListPrice < 1000 THEN 'Under $1000'
ELSE 'Over $1000'
ORDER BY ProductNumber ;