A query that contains LIKE search criteria that start with a wildcard cannot benefit from indexes for that part of the search. The query engine will have to do a slow traversal through the whole of the database (or at least the relevant part of the database, depending on the other search criteria) and do a regex or substring search on that field for each record.
in reply to s/Perl/SQL/ ?
A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James
My blog: Imperial Deltronics