A Simple Use of Case Statement in SQL Server 2012

In this article, I would like to show the most commonly used case expression in SQL Server. CASE is the special scalar expression or conditional statement in the SQL language which returns a single value based on the evaluation of a statement. Case statements can be used in Select and Where clauses and even an Order By clause. A Case expression is mostly used in SQL stored procedures or as a formula for a particular column, which optimizes the SQL statements. So let's take a look at a practical example of how to use a case statement in SQL Server 2012. The example is developed in SQL Server 2012 using the SQL Server Management Studio.

 

We'll start by walking through a simple case statement. The Case statement can be used in two forms in SQL Server:

1. Case statement with simple expression.
2. Case statement with comparison or searched expression.

Case statement with simple expression

 

The Simple Case expression checks only for equivalent values and cannot contain Boolean expressions. A Simple Case Expression looks for the first expression in the list of all when the clause that matches expression_1 and evaluates the corresponding when clause. If there is no match, then the else clause is evaluated. The general syntax of the Simple CASE expression is:

 

CASE expression

WHEN exp_1 THEN result_1

[WHEN exp_2 THEN result_2]

[..................]

[WHEN exp_n THEN result_n]

[ELSE expression]

END

 

Example

DECLARE @Name varchar(50)
SET @Name = 'Rohatash'
SELECT
Case  @Name
 WHEN  'Deepak'  THEN  'Name Deepak'
 WHEN  'Manoj' THEN  'Name Found Manoj'
 WHEN  'Rohatash' THEN   'Name Found Rohatash'
ELSE 'Name not Found'
END

Output

 

 

 

Now replace the name Rohatash kumar in place of Rohatash.

 

Example

DECLARE @Name varchar(50)
SET @Name = 'Rohatash'
SELECT
Case  @Name
 WHEN   'Deepak'  THEN  'Name Found Deepak'
 WHEN ' Manoj' THEN  'Name Found Manoj'
 WHEN  'Rohatash Kumar' THEN   'Name Found Rohatash'
ELSE 'Name not Found'
END

Output

 

 

 

Case statement with comparison or searched expression

 

The Searched Case expression contains Boolean expressions or comparison operators. In the following example we will see how to use a searched expression with comparison operators.

 

The general syntax of the searched CASE expression is:

 

CASE

WHEN condition_1 THEN result_1

[WHEN condition_2 THEN result_2]

[..................]

[WHEN condition_n THEN result_n]

[ELSE expression]

[else result_n]

END

 

Creating a table in SQL Server

create table student
(
stu_id int,
stu_name varchar(20),
marks int
);

Now inserting rows values into the student table:

Insert into student values('101','ravi','65');
Insert into student values('102','sumit','32');
Insert into student values('103','rekha','76');
Insert into student values('104','Yong','34');
Insert into student values('105','Hem','78');

The Student table looks like this:

 

 

 

In the above table students Id, Name and their marks are given. Now I want the following output with the help of a CASE statement:

 

Stu_Id	Stu_Name	Marks	Remarks	Grade
101	Ravi	65	Pass	A
102	Sumit	32	Fail	E
103	Rekha	76	Pass	A +
104	Yong	34	Pass	E
105	Hem	78	Pass	A+

 

Using CASE Expression

Select Stu_Id,Stu_Name,Marks,
Case When Marks > 32 Then 'Pass' Else 'Fail'
End as Remarks,
Case When Marks >= 76 Then 'A+'
        When Marks >= 65 Then 'A'
        When Marks < 35 Then 'E'
End as Grade
From Student

Output

 

 

 

Case Statement with where condition

Select Stu_Id,Stu_Name,Marks,
Case When Marks > 32 Then 'Pass' Else 'Fail'
End as Remarks,
Case When Marks >= 76 Then 'A+'
        When Marks >= 65 Then 'A'
        When Marks < 35 Then 'E'
End as Grade
From Student where marks< 35

Output

 

 

 

Case Statement with Order by clause

Select Stu_Id,Stu_Name,Marks,
Case When Marks > 32 Then 'Pass' Else 'Fail'
End as Remarks,
Case When Marks >= 76 Then 'A+'
        When Marks >= 65 Then 'A'
        When Marks < 35 Then 'E'
End as Grade
From Student order by Marks