ereg(i) for form input validation for SQL - tutorial?

Does anyone know of a good tutorial for using ereg and eregi to validate standard fields for SQL input (i'm using PearDB). Typically the type of validation that I think I need would be, firstly to detect invalid characters, or special characters, or things that can screw up the SQL Query. Others would be the alpha only, string lengths, email address, dates and times, phone numbers. These are standard items in a lot of systems...surely there's a tutorial out there somewhere, or a sample script or something. I've only just discovered regex, so its all a bit hmmmmmmmm at the moment. Any links for tutorials or sample scripts would be much appreciated. Thanks Simon H