ALTER TABLE to add a composite primary key

Question

I have a table called provider. I have three columns called person, place, thing. There can be duplicate persons, duplica

Answer 1

You may simply want a UNIQUE CONSTRAINT. Especially if you already have a surrogate key. (example of an already existing surrogate key would be a single column that is an AUTO_INCREMENT )

Below is the sql code for a Unique Constraint

ALTER TABLE `MyDatabase`.`Provider`
    ADD CONSTRAINT CK_Per_Place_Thing_Unique UNIQUE (person,place,thing)
;