double primary index & history

[BEFOR]

I have a table with two primary index columns. To maintain an edit history, this is first updating a users existing "fourth col" below and setting it to "0", then inserting "1" into this new row:

first col - users primary id/by session
second col - primary id brought from a table join value.
third col - CURRENT_DATE
fourth active col - "0" for inactive, "1" for active.

The update sets a prior user values of fourth col to "o" . No problem.

But when more rows are inserted, everything goes until same values as the prior ones are attempted in the "second col" (primary id). Erroring:

"Duplicate entry '50-2007' for key 1 " or something like this. It won't take same values twice.

Can anyone make a suggestion? Can I make the third col a primary index to make each row unique? - though I'd prefer not to (running queries).

[superwormy]

To the best of my knowledge... you can't have two primary indexes on a table.

Do you mean you have a query which JOINs two tables so that a primary key from each table shows up? Can we see the query/table structure?

[BEFOR]

-- Table structure for table TheTable

CREATE TABLE Thetable (
first col int(6) NOT NULL default '0',
second col int(10) NOT NULL default '0',
third col date default '0000-00-00',
fourth active col int(3) default '0',
PRIMARY KEY (first col,second col)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Sorry, maybe should have said "two index columns that form a primary key"?
'second col' is not a primary key from another table.