Sql Server: Using CASE Statement inside IN Clause (alternative)

Introduction:  In this article I am going to share best alternative of using CASE statement inside IN operator in sql server with suitable examples.

In previous articles i explained the articles of Using case expression in select statement in sql server and Try catch to handle exception and commit/rollback transaction and Remove duplicate records/data from sql server database table and Create database script and create database from that script and Drop or truncate parent table by dropping all foreign key constraints

Description: While working with sql server database I got the following requirement.

I was to get the permissions according to user type. i.e.

• If UserType=1 then permission will be Read & Write, Update and Delete.
• If UserType=2 then permission will be Read & Write, Update.
• If UserType=3 then permission will be Read Only.

Here UserType=1:Admin,  2: User,  3: Guest User

Implementation: Let’s create PermissionType table and insert data in it using following script.

CREATE TABLE tbPermissionType

(

            PermissionId               INT IDENTITY(1,1) PRIMARY KEY,

            PermissonType            VARCHAR(100)          

)

INSERT INTO tbPermissionType VALUES('Read Only')

INSERT INTO tbPermissionType VALUES('Read & Write')

INSERT INTO tbPermissionType VALUES('Update')

INSERT INTO tbPermissionType VALUES('Delete')

Check table data

SELECT * FROM tbPermissionType

PermissionId	PermissionType
1	Read Only
2	Read & Write
3	Update
4	Delete

To get what I need I first I tried using CASE inside IN Clause that first came up in my mind.

DECLARE @UserType TINYINT=1;

SELECT PermissonType FROM tbPermissionType

WHERE  PermissionId IN (CASE WHEN @UserType=1 THEN (2,3,4)

                                                   WHEN @UserType=2 THEN (2,3)

                                                   WHEN @UserType=3 THEN (1) END

                                          )

But I got the following error:

Incorrect syntax near ','.

Then I searched on google and got many ways to get this done. I tried many ways and found the result I need. But then I tried much efficient and clear way without using CASE statement that I am going to share.

Let’s try by passing 1, 2, 3 value to the UserType variable and see whether we get the desired result or not.

Execute the following by passing UserType=1:

DECLARE @UserType TINYINT=1;

SELECT PermissonType FROM tbPermissionType

WHERE

(@UserType = 1 AND PermissionId IN (2,3,4))        

OR

(@UserType =2 AND PermissionId IN (2,3))

OR

(@UserType =3 AND PermissionId=1)

Result will be as expected.

PermissionType

Read & Write

Update

Delete

Now execute the following by passing UserType=2

DECLARE @UserType TINYINT=2;

SELECT PermissonType FROM tbPermissionType

WHERE

(@UserType = 1 AND PermissionId IN (2,3,4))        

OR

(@UserType =2 AND PermissionId IN (2,3))

OR

(@UserType =3 AND PermissionId=1)

Result will be as expected.

PermissionType

Read & Write

Update

Now execute the following by passing UserType=3

DECLARE @UserType TINYINT=3;

SELECT PermissonType FROM tbPermissionType

WHERE

(@UserType = 1 AND PermissionId IN (2,3,4))        

OR

(@UserType =2 AND PermissionId IN (2,3))

OR

(@UserType =3 AND PermissionId=1)

Result will be as expected.

PermissionType

Read Only

So it is clear  from the result that without using CASE Statement we can get the result in efficient way.

 Now over to you:

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