Unique constraint on varchar field

Question

Hi How to add unique constraint on varchar field. For Ex in my table company name should be unique.. I dont want the user to enter duplicate values

Pravin More · Answer

HI  You cannot put a unique constraint on a VARCHAR(MAX) column (which could be up to 2 GB of text!!). 320 chars is the max length. Thanks Pravin.

Priya Linge · Answer

Hi CREATE TABLE Persons ( P_Id int CompanyName varchar(255) CONSTRAINT Companyname_person UNIQUE(CompanyName)) select * from Persons insert into Persons values(1'XYZ') insert into Persons values(2'XYZ')----At this stage it gives the message Msg 2627 Level 14 State 1 Line 2 Violation of UNIQUE KEY constraint 'Comapnyname_person'. Cannot insert duplicate key in object 'dbo.Persons'. The statement has been terminated. Hope this will help you. Thanks.