HOW TO: select only the last record in a mySQL table.

I'm not very good in mySQL but am trying to modify a php script.
It has to do with a log function using a mySQL table to store the log
entries.
I want to retrieve the last log record (if any) and if the last log
entry is the same as my current (to be) entry, simply update the time in
the last entry. But if not, simply insert the new entry.

My question is how to select the last entry from the log table?

I know that I can select all and get the number of rows and then
select just the last with a LIMIT of N,1.
But is there a better, more efficient way?

CREATE TABLE log (
id mediumint(8) unsigned NOT NULL auto_increment,
time varchar(20) NOT NULL,
entry varchar(255) NOT NULL,
PRIMARY KEY (id)
);

Thanks.



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