Using Case With Select and Update Statement in SQL Server 2012

In this article, I would like to show the most commonly used case expressions with update statements 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.  In this article, you use case with an update statement.  So let's have a look at a practical example of how to use a case with Update 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.

 

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: 

 

 

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 the "when" clauses that matches the expression and evaluates the corresponding when clause. If there is no match, then the else clause is evaluated (if it exists). 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

Case Expression with Select Statement

 

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

 

In the above table the student's 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

 

 

Using CASE Expression with Update Statement

 

In the following table the student's Id, Name and their marks and Remarks are given.

 

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

 

Now I want the following output with the help of a CASE statement: 

 

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

 

You can see in the above remarks column of the student table which contain Records as Pass or Fail. Your task is to write a query which will change the Remarks Pass to Fail and Fail to Pass. Now I want the preceding output with the help of a CASE statement: 

update Student
set Remarks =
CASE WHEN Remarks='Pass' THEN 'Fail'
When Remarks='Fail' THEN 'Pass'
End
select * from Student

Now press F5 to execute the query.

 

Output