Export (0) Print
Expand All
ABS
ALL
AND
ANY
AVG
bit
COS
COT
DAY
EXP
GO
IN
LEN
LOG
MAX
MIN
NOT
OR
PI
SET
SIN
STR
SUM
TAN
USE
VAR
Expand Minimize
47 out of 69 rated this helpful - Rate this topic

CASE

SQL Server 2000

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)

See Also

Data Type Conversion

Data Types

Expressions

SELECT

System Functions

UPDATE

WHERE

Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft. All rights reserved.