How do I specify unique constraint for multiple columns in MySQL?

mysql unique-constraint composite-key database-table
Niyaz picture Niyaz · Mar 11, 2009 · Viewed 519.2k times · Source

I have a table:

table votes (
    id,
    user,
    email,
    address,
    primary key(id),
);

Now I want to make the columns user, email, address unique (together).

How do I do this in MySql?

Of course the example is just... an example. So please don't worry about the semantics.

Answer

jonstjohn picture jonstjohn · Mar 11, 2009 
ALTER TABLE `votes` ADD UNIQUE `unique_index`(`user`, `email`, `address`);

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