O'Reilly logo
  • miraj Desai thinks this is interesting:

A lookup table is created in much the same way as is any other table. The difference lies in the choice of the primary key. Every table we’ve created so far has had a column named id that was designated to be the PRIMARY KEY when the table was created. Designating a column as a primary key tells MySQL to forbid two entries in that column from having the same value. It also speeds up join operations based on that column.