Presently, the GUI mode only let's you use bulk update if your table has a single-column primary key in MySQL. However, for some data sets a composite primary key is the choice we have available. Using only a single column for the update would not correctly identify the record to update. Take the following simple example:
CREATE TABLE foo ( user_id int(10) unsigned not null, location_id int(10) unsigned not null, rating int(3) unsigned not null, PRIMARY KEY(user_id, location_id) )
In this case, I'd like to update based on the tuple of user_id and location_id, either one is insufficient to identify the record on its own.