CASE
Evaluates a list of conditions and returns one of multiple possible result expressions.
CASE has two formats:
- The simple CASE function compares an expression to a set of simple expressions to determine the result.
- The searched CASE function evaluates a set of Boolean expressions to determine the result.
Both formats support an optional ELSE argument.
Syntax
Simple CASE function:
CASE input_expression
WHEN when_expression THEN result_expression
[ ...n ]
[
ELSE else_result_expression
]
END
Searched CASE function:
CASE
WHEN Boolean_expression THEN result_expression
[ ...n ]
[
ELSE else_result_expression
]
END
Arguments
input_expression
Is the expression evaluated when using the simple CASE format. input_expression is any valid Microsoft® SQL Server™ expression.
WHEN when_expression
Is a simple expression to which input_expression is compared when using the simple CASE format. when_expression is any valid SQL Server expression. The data types of input_expression and each when_expression must be the same or must be an implicit conversion.
n
Is a placeholder indicating that multiple WHEN when_expression THEN result_expression clauses, or multiple WHEN Boolean_expression THEN result_expression clauses can be used.
THEN result_expression
Is the expression returned when input_expression equals when_expression evaluates to TRUE, or Boolean_expression evaluates to TRUE. result expression is any valid SQL Server expression.
ELSE else_result_expression
Is the expression returned if no comparison operation evaluates to TRUE. If this argument is omitted and no comparison operation evaluates to TRUE, CASE returns NULL. else_result_expression is any valid SQL Server expression. The data types of else_result_expression and any result_expression must be the same or must be an implicit conversion.
WHEN Boolean_expression
Is the Boolean expression evaluated when using the searched CASE format. Boolean_expression is any valid Boolean expression.
Result Types
Returns the highest precedence type from the set of types in result_expressions and the optional else_result_expression. For more information, see Data Type Precedence.
Result Values
Simple CASE function:
- Evaluates input_expression, and then, in the order specified, evaluates input_expression = when_expression for each WHEN clause.
- Returns the result_expression of the first (input_expression = when_expression) that evaluates to TRUE.
- If no input_expression = when_expression evaluates to TRUE, SQL Server returns the else_result_expression if an ELSE clause is specified, or a NULL value if no ELSE clause is specified.
Searched CASE function:
- Evaluates, in the order specified, Boolean_expression for each WHEN clause.
- Returns result_expression of the first Boolean_expression that evaluates to TRUE.
- If no Boolean_expression evaluates to TRUE, SQL Server returns the else_result_expression if an ELSE clause is specified, or a NULL value if no ELSE clause is specified.
Examples
A. Use a SELECT statement with a simple CASE function
Within a SELECT statement, a simple CASE function allows only an equality check; no other comparisons are made. This example uses the CASE function to alter the display of book categories to make them more understandable.
USE pubs
GO
SELECT Category =
CASE type
WHEN 'popular_comp' THEN 'Popular Computing'
WHEN 'mod_cook' THEN 'Modern Cooking'
WHEN 'business' THEN 'Business'
WHEN 'psychology' THEN 'Psychology'
WHEN 'trad_cook' THEN 'Traditional Cooking'
ELSE 'Not yet categorized'
END,
CAST(title AS varchar(25)) AS 'Shortened Title',
price AS Price
FROM titles
WHERE price IS NOT NULL
ORDER BY type, price
COMPUTE AVG(price) BY type
GO
Here is the result set:
Category Shortened Title Price
------------------- ------------------------- --------------------------
Business You Can Combat Computer S 2.99
Business Cooking with Computers: S 11.95
Business The Busy Executive's Data 19.99
Business Straight Talk About Compu 19.99
avg
==========================
13.73
Category Shortened Title Price
------------------- ------------------------- --------------------------
Modern Cooking The Gourmet Microwave 2.99
Modern Cooking Silicon Valley Gastronomi 19.99
avg
==========================
11.49
Category Shortened Title Price
------------------- ------------------------- --------------------------
Popular Computing Secrets of Silicon Valley 20.00
Popular Computing But Is It User Friendly? 22.95
avg
==========================
21.48
Category Shortened Title Price
------------------- ------------------------- --------------------------
Psychology Life Without Fear 7.00
Psychology Emotional Security: A New 7.99
Psychology Is Anger the Enemy? 10.95
Psychology Prolonged Data Deprivatio 19.99
Psychology Computer Phobic AND Non-P 21.59
avg
==========================
13.50
Category Shortened Title Price
------------------- ------------------------- --------------------------
Traditional Cooking Fifty Years in Buckingham 11.95
Traditional Cooking Sushi, Anyone? 14.99
Traditional Cooking Onions, Leeks, and Garlic 20.95
avg
==========================
15.96
(21 row(s) affected)
B. Use a SELECT statement with simple and searched CASE function
Within a SELECT statement, the searched CASE function allows values to be replaced in the result set based on comparison values. This example displays the price (a money column) as a text comment based on the price range for a book.
USE pubs
GO
SELECT 'Price Category' =
CASE
WHEN price IS NULL THEN 'Not yet priced'
WHEN price < 10 THEN 'Very Reasonable Title'
WHEN price >= 10 and price < 20 THEN 'Coffee Table Title'
ELSE 'Expensive book!'
END,
CAST(title AS varchar(20)) AS 'Shortened Title'
FROM titles
ORDER BY price
GO
Here is the result set:
Price Category Shortened Title
--------------------- --------------------
Not yet priced Net Etiquette
Not yet priced The Psychology of Co
Very Reasonable Title The Gourmet Microwav
Very Reasonable Title You Can Combat Compu
Very Reasonable Title Life Without Fear
Very Reasonable Title Emotional Security:
Coffee Table Title Is Anger the Enemy?
Coffee Table Title Cooking with Compute
Coffee Table Title Fifty Years in Bucki
Coffee Table Title Sushi, Anyone?
Coffee Table Title Prolonged Data Depri
Coffee Table Title Silicon Valley Gastr
Coffee Table Title Straight Talk About
Coffee Table Title The Busy Executive's
Expensive book! Secrets of Silicon V
Expensive book! Onions, Leeks, and G
Expensive book! Computer Phobic And
Expensive book! But Is It User Frien
(18 row(s) affected)
C. Use CASE with SUBSTRING and SELECT
This example uses CASE and THEN to produce a list of authors, the book identification numbers, and the book types each author has written.
USE pubs
SELECT SUBSTRING((RTRIM(a.au_fname) + ' '+
RTRIM(a.au_lname) + ' '), 1, 25) AS Name, a.au_id, ta.title_id,
Type =
CASE
WHEN SUBSTRING(ta.title_id, 1, 2) = 'BU' THEN 'Business'
WHEN SUBSTRING(ta.title_id, 1, 2) = 'MC' THEN 'Modern Cooking'
WHEN SUBSTRING(ta.title_id, 1, 2) = 'PC' THEN 'Popular Computing'
WHEN SUBSTRING(ta.title_id, 1, 2) = 'PS' THEN 'Psychology'
WHEN SUBSTRING(ta.title_id, 1, 2) = 'TC' THEN 'Traditional Cooking'
END
FROM titleauthor ta JOIN authors a ON ta.au_id = a.au_id
Here is the result set:
Name au_id title_id Type
------------------------- ----------- -------- -------------------
Johnson White 172-32-1176 PS3333 Psychology
Marjorie Green 213-46-8915 BU1032 Business
Marjorie Green 213-46-8915 BU2075 Business
Cheryl Carson 238-95-7766 PC1035 Popular Computing
Michael O'Leary 267-41-2394 BU1111 Business
Michael O'Leary 267-41-2394 TC7777 Traditional Cooking
Dean Straight 274-80-9391 BU7832 Business
Abraham Bennet 409-56-7008 BU1032 Business
Ann Dull 427-17-2319 PC8888 Popular Computing
Burt Gringlesby 472-27-2349 TC7777 Traditional Cooking
Charlene Locksley 486-29-1786 PC9999 Popular Computing
Charlene Locksley 486-29-1786 PS7777 Psychology
Reginald Blotchet-Halls 648-92-1872 TC4203 Traditional Cooking
Akiko Yokomoto 672-71-3249 TC7777 Traditional Cooking
Innes del Castillo 712-45-1867 MC2222 Modern Cooking
Michel DeFrance 722-51-5454 MC3021 Modern Cooking
Stearns MacFeather 724-80-9391 BU1111 Business
Stearns MacFeather 724-80-9391 PS1372 Psychology
Livia Karsen 756-30-7391 PS1372 Psychology
Sylvia Panteley 807-91-6654 TC3218 Traditional Cooking
Sheryl Hunter 846-92-7186 PC8888 Popular Computing
Anne Ringer 899-46-2035 MC3021 Modern Cooking
Anne Ringer 899-46-2035 PS2091 Psychology
Albert Ringer 998-72-3567 PS2091 Psychology
Albert Ringer 998-72-3567 PS2106 Psychology
(25 row(s) affected)