Question

How do I make it so 2 columns cannot have the same data. My table consists of 3 fields.

studentid    id_project     level_of_want
1            2                high
1            3                low
1            4                high
1            2                low

I want is so that one column can have the same data (eg 1 in studentid) but the studentid and id_project cannot have the same data more than once (enties 1 and 4 above). studentid can be 1 and id_project can be 1, but this can only happen once.

Answer 1

You need to add an “unique” index.

Read http://dev.mysql.com/doc/refman/5.0/en/create-index.html

create unique index my_index on my_table (studentid, id_project);