SQL question

[James Traynor]

I am running some queries on the tables created by the xapdblogger
(mysql) and have come across an oddity that there is probably a really
simple explanation to.


select header_id from messageheader where
source="mi4.weather.egll"
order by header_id desc limit 1;

takes 9 seconds

select header_id from messageheader where source='mi4.weather.egll'
order by header_id desc limit 1;

takes .05 seconds

what does the " do that the ' doesn't ??

Thanks

James