How to add unique constraint to existing table in Sqlite?

Question

I have an existing table in Sqlite. How do I add a unique constraint to it?

Answer 1

I am assuming you are using SQLiteManager from FireFox, please create the table again, normally it doesn't allow to change the constraints when you have already created a table.

NOTE - It can be done using code too, this is another way of doing it..

Edited See the image below

Answer 2

You can't add a constraint to existing table in SQLite,(In SQL there is a option for do that). You need to re-create the table with necessary contraints.

There is only a few option available for alter table command in sqlite. Please check the image:

Also check Sqlite org reference.

---

EDIT

However you can add unique index for your table to achieve the same effect. So you can use the following query to achieve that:

CREATE UNIQUE INDEX your_unique_index ON your_table(column_name);

In most cases, UNIQUE and PRIMARY KEY constraints are implemented by creating a unique index in the database.

Reference : SQLite Constraints

Answer 3

You can add constraint by creating unique index:

CREATE UNIQUE INDEX ux_friend_name ON friend(name);

where ux_friend_name is unique index name, friend(name) - table and its columns that will be affected by this constraint.

You can read more here.