9. Presence Check

There might be an important piece of data that you want to make sure is always stored.

For example, a school will always want to know an emergency contact number, a video rental store might always want to know a customer's address, a wedding dress shop might always want a record of the brides wedding date.

A presence check makes sure that a critical field cannot be left blank, it must be filled in. If someone tries to leave the field blank then an error message will appear and you won't be able to progress to another record or save any other data which you have entered.