Custom function in MySQL comes handy if we have some sort of calculation what to make, in order to get a value what can be stored. This implies that we want to push some logic into the database which is not a to popular idea among engineers. A function always gives one value as a result like ‘select pi(); gives us 3.141593’. To create a function the type of the input value(s) need to be specified as well as the output, result.

I was lucky and I had the chance to study MySQL (&PHP basics) on a 20 week full-time course, with a Tutor who had 15+years experience in web development. He really guided us if something was not clear. Unfortunately nowadays most people just start at home google the subject and start to pick it up. I do/did the same with couple of IT subject but the problem comes if you hurry to have something in your hand to work with and then you fly over things would be a MUST.

Did you ever notice that MySQL auto increment used as default value to write in, if column value is null (or not specified). This is a really great feature, used I think in 80% of tables as id. If you delete the last row of a table eg. where id=5, time comes for inserting a new record with ‘null’ as id value, auto_increment gives id=6 as next to use. In other words if we delete a row auto increment can’t pick up the deleted values.