Error 1068: Multiple primary key defined

Possible Causes and Solutions

No more than one primary key can be defined per table. Attempting to define more in a single table will result in this error. For example:

CREATE TABLE t1(
    c1 INT NOT NULL AUTO_INCREMENT, 
    c2 INT NOT NULL, 
    PRIMARY KEY(c1),
    PRIMARY KEY(c2)
);
ERROR 1068 (42000): Multiple primary key defined

CREATE TABLE t1(
    c1 INT NOT NULL AUTO_INCREMENT, 
    c2 INT NOT NULL, 
    PRIMARY KEY(c1)
);

It's also possible that this this error results from a mistaken attempt to define a multi-part primary key. This is an example of the correct definition for such a key.

CREATE TABLE t1(
    c1 INT NOT NULL AUTO_INCREMENT, 
    c2 INT NOT NULL, 
    PRIMARY KEY(c1, c2)
);