Alter combination of 2 existing columns as a unique key

[James]

To alter 1 column to a unique key,

ALTER TABLE user MODIFY COLUMN id INT NOT NULL UNIQUE;

But how to set combination of 2 columns as a unique key?
Individual keys are not unique, but combination is.

TIA,
James

[Gordon Burditt]

Post by James
To alter 1 column to a unique key,
ALTER TABLE user MODIFY COLUMN id INT NOT NULL UNIQUE;
But how to set combination of 2 columns as a unique key?
Individual keys are not unique, but combination is.

ALTER TABLE user ADD UNIQUE (id,domain);

That just adds an index. You might need to drop an old one first. Or not.