mySQL could/would cache that data in memory if the table is used often, however you lose speed if the MySQL server is on a different machine than the script. If you have a select for each ID you gain speed again though, specially when the cache becames larger. I think a SQL server is a good way to go.

Don't use LIKE though, use =, although LIKE without % and ? might be optimized that way by the server... dunno.

use numeric fields if possible, if not, then create a index on a substring of the id. for example,

id char(10), Update: don't use varchar ...
index index_id id(3)


Tiago