Column in table is of a type that is invalid for use as a key column in an index
sql, sql-server, sql-server-2008
Solution
An index's key cannot exceed a total size of 900 bytes. Change the data type to `NVARCHAR(450)`. If that is not suitable, use a surrogate key (typically an `IDENTITY` column).
Problem
I have a table where I am storing employee details. I want to alter the table and set one of the column `emp_code` as primary key. Its datatype is `nvarchar(max)`, but I am not able to set it as primary key. I run the following query : ``` ALTER TABLE user_master ADD PRIMARY KEY (emp_code) ``` but it gives me an error : Msg 1919, Level 16, State 1, Line 1 Column `emp_code` in table `user_master` is of a type that is invalid for use as a key column in an index. Msg 1750, Level 16, State 0, Line 1 Could not create constraint. See previous errors. How can I overcome this?