Does any body know how to create a user defined function in mysql that would achieve the following:

select id from sometable where a_fuction(some_field, 'some string') = 1;

a_fuction is the user defined function name
some_field is the field which needs to be searched
'some string' is user provided search string which needs to be searched

Basicaly what would the internal query of this fuction consist of to search a user provided search string and produce a boolean 0 or 1

don't re-invent the wheel

use LIKE

As rudy says:
However, should you wish to do it you can use a CREATE FUNCTION in MySQL 5+ to take the field name and string and produce a returned result based on whether it exists or not.
I doubt that'll you'll be able to be able to write a better algorithm than already exists. That and you won't be able to use indexes like MySQL's internal procedures will, but by all means give it a go and let us know how you get on.