php script to search mysql database on multiple keywords

This program will search a MySQL database to match keyword(s) entered by the visitor. The visitor can choose to have the results returned as an 'exact' match (nice and easy to program for), match 'any' keywords (which will return a record if any of the keywords are present in the searched fields) or match 'all' keywords (the most difficult to program for but the most useful - isn't it always the way!). It was developed on a Windows / Apache platform but should work on many others. I've scattered comments everywhere to explain what's going on. I hope they help.