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A Simple Use of SQL CASE Expression

, 19 Aug 2009
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This article will give you an idea about how to use CASE expression in T-SQL or as a formula of a particular column.

Table of Contents

Introduction

This article will give you an idea about how to use CASE expression in T-SQL or as a formula of a particular column.

What is CASE Expression 

CASE is the special scalar expression in SQL language. CASE expression is widely used to facilitate determining / setting a new value from user input values. CASE expression can be used for various purposes which depends on the business logic.

CASE expression is mostly used in SQL stored procedure or as a formula for a particular column, which optimizes the SQL statements.

Syntax of CASE Expression 

SQL CASE expression is used as a type of IF-THEN-ELSE statement. It is similar to switch statement in recent programming languages such as C# and Java. The syntax of the CASE statement is simple as follows:

1.    CASE column_name  
2.      WHEN condition1 THEN result1  
3.      WHEN condition2 THEN result2  
4.      ...  
5.      ELSE result  
6.    END

Sample Example of CASE Statement 

DECLARE @intInput INT
SET @intInput = 2
SELECT CASE(@intInput) WHEN 1 THEN 'One' WHEN 2 THEN 'Two' _
		WHEN 3 THEN 'Three' ELSE 'Your message.' END 

Use of CASE Expression

The case expression can be used anywhere scalar expressions are allowed, including in WHERE and HAVING clauses of the select statement.

In this article, I would like to show the most commonly used case expression in:

  • Stored procedure 
  • Formula of a particular column 
  • View

Basic Use in a Stored Procedure

A simple example of using CASE in a stored procedure is given below:

-- =============================================
-- Author: Md. Marufuzzaman
-- Create date: 
-- Description:    A simple example of CASE expression.
-- =============================================
/*
DECLARE @varCountry VARCHAR(100)
EXEC spGetCountry 1, @varCountry OUTPUT
SELECT @varCountry
*/

ALTER PROCEDURE [dbo].[spGetCountry]
 @intCode        INT
,@varOutPut         VARCHAR(100) OUTPUT
AS
BEGIN
 
SELECT CASE(@intCode) WHEN 1 THEN 'Country_1'
              WHEN 2 THEN 'Country_2'
              WHEN 3 THEN 'Country_3'
              WHEN 4 THEN 'Country_4'
              WHEN 5 THEN 'Country_5'
              WHEN 6 THEN 'Country_6'
              WHEN 7 THEN 'Country_7'
              WHEN 8 THEN 'Country_8'
              WHEN 9 THEN 'Country_9'
              WHEN 10 THEN 'Country_10'         
                      ELSE 'Unknown' END  
      
END

Basic Use in a Table Column Formula

When we create a Table in design mode, SQL server provides us the properties of each column, where we can set various property values like a default value of a column, identity of a column, etc. Every column has a special property that is a custom formula, where you can set your own formula for data manipulation. Let’s take an example:

Our target is to write a formula for a column, and this formula is responsible for setting a new value for another column.

Figure 1 - How we can set a formula for a particular column

A simple example of using CASE in a Table column formula is given below:

// SQL CASE statement
(case [Code] when (1) then 'Country_1' when (2) then 'Country_2' _
	when (3) then 'Country_3' when (4) then 'Country_4' when (5) _
	then 'Country_5' when (6) then 'Country_6' when (7) then 'Country_7' _
	when (8) then 'Country_8' when (9) then 'Country_9' when (10) _
	then 'Country_10' else 'Unknown' end)

When you insert / update a value at column “code”, the SQL server will fire the formula which is associated with the column “code” and finally set the value of that particular column.

Output
Figure 2 - How column "Country" sets value when column code value is inserted / updated

Basic Use in a View

There is nothing new to use CASE expression in a view object. As I mentioned before, CASE expression can be used anywhere scalar expressions are allowed, including in WHERE and HAVING clauses of the select statement.

Conclusion 

I hope that you will get an idea about how to use CASE expression. Enjoy!

History

  • 18th August 2009: Initial post

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Md. Marufuzzaman
CEO
Bangladesh Bangladesh
A highly experienced leader with successful track record of software development, product innovations, brand management and corporate communication etc. Some successful product innovations have also achieved and awards “Most Valuable Professional” (MVP) at 2010 and 2011 by codeproject.com and also selected as a mentor of codeproject.com. Published over 100 technical articles in various software development resource sites (i.e., codeprojetc.com, Microsoft MSDN, and IEEE & IBM (In progress)) and various IT Forums, Blogs etc.
 
Over ten years of professional experiences in ICT field having extensive experience in formulating corporate vision and long term strategy. Leading development related functions including design, development, services, data management and analytics, customer experience management, content services, digital analytics and optimization.
 
An individual with results-driven approach and relentless in pursuit of excellence from a business and organizational standpoint. Believes in transparency, commitment and teamwork.
 
Expertise: Software/Solution Architect, SaaS platform base application, Large scale win32/web based business software solutions, enterprise applications, integration, etc.
 
Technologies/Tools: Microsoft.Net version 05/08/10/12, Microsoft SQL Server version 7/2K/05/08/12 , Oracle version 10/11, MySql version 5.1, 5.5, PS2, Visual C#, R, VB.NET, ASP.NET, PHP, API, MVC, WebAPI , Add-In Visual Basic etc.,. I have also more than two years’ of strong experience in mobile-VAS (platform development).
 
Points of Interest: Technology and research & development especially focused on business functionalities and social business areas as well, few stuff including:
 
1.R&D on new techniques as required to increase business revenue.
2.Urban and rural sectors to improve people’s lifestyle, better medical facilities, education, social business etc., using innovative technical solutions.
3.Research and innovative product development.
4.Etc.
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Comments and Discussions

 
GeneralMy vote of 4 PinprofessionalPratik Bhuva16-Dec-13 1:55 
GeneralMy vote of 5 Pinmemberkarthik reddy mereddy10-Sep-13 22:41 
Questionhow to give Multiple expressions PinmemberPhanindraTSK15-Jul-13 21:11 
AnswerRe: how to give Multiple expressions PinmentorMd. Marufuzzaman15-Jul-13 23:30 
GeneralMy vote of 5 PinmemberAndrewOkoth25-Apr-13 21:43 
GeneralRe: My vote of 5 PinmentorMd. Marufuzzaman15-Jul-13 23:31 
GeneralMy vote of 5 PinmemberTasnia.Maruf20-Sep-10 0:26 
Good work
GeneralRe: My vote of 5 PinmvpMd. Marufuzzaman3-Oct-10 4:13 
GeneralMy vote of 1 Pinmembergrandtree29-Apr-10 16:05 
GeneralCase syntax PinmemberMember 150309625-Aug-09 21:27 
GeneralRe: Case syntax PingroupMd. Marufuzzaman26-Aug-09 0:35 
GeneralRe: Case syntax PingroupMd. Marufuzzaman26-Aug-09 0:35 
GeneralRe: Case syntax PingroupMd. Marufuzzaman26-Aug-09 0:49 
GeneralYou are doing great ! PinmvpAbhijit Jana19-Aug-09 5:36 
GeneralRe: You are doing great ! PingroupMd. Marufuzzaman19-Aug-09 7:22 

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