Change an existing column to unique

[yigalm]

Hi,

What is the syntax in SQL to change an existing column to be unique, but not create a new unique column?

 

[tlbroadbent]

The T-SQL syntax is as follows.

Alter Table Table_Name
Add Constraint Constraint_Name Unique(Column_Name)

Example:

Alter Table dbo.employees
Add constraint EmpNo_Unique Unique(EmpNo) Terry L. Broadbent
Life would be easier if I had the source code. -Anonymous

 

[RickCole]

Use the SQL Alter Table command with Constraint and Unique.

Rick Cole

 

[yigalm]

What is the constraint_name?

alter table pr2_users_values
add constraint <constraint name> unique (f_login);

This is what I have now, but what do I put for constraint_name?

 

[tlbroadbent]

Constraint_name is just a name for the constraint. It can be whatever you determine is best. Terry L. Broadbent
Life would be easier if I had the source code. -Anonymous

 

[yigalm]

It says: Error 1061: Duplicate keyname 'F_Login'

 

[tlbroadbent]

Which version of SQL Server are you running?

Do you have a key, index or constraint with the same name? Try using a different name? Terry L. Broadbent
Life would be easier if I had the source code. -Anonymous

 

[yigalm]

I am running MySQL.
When I say:
show create table pr2_users_values;

It lists this and all the other fields:
'F_Login' varchar(99) NOT NULL default ''

and at the bottom it says:
KEY 'F_Login' ('F_Login')

 

[tlbroadbent]

This is a MS SQL Server forum. The syntax may not always be compatible with MySQL. May I suggest moving your question to a MySQL forum or checking the MySQL website for the answer.

http://www.mysql.com

Terry L. Broadbent
Life would be easier if I had the source code. -Anonymous