Re: Re: SQL Queries

Hello, That kind of queries usually run faster using a LEFT JOIN, like this: select u.id from users u left join notes n on u.id = n.user_id where n.id is null; That query will give you the ids of the users without notes. Make sure to have an index on notes.user_id to let the LEFT JOIN use it and run faster. Hope that helps, regards, Jonathan On Sun, Dec 20, 2009 at 6:41 PM, דניאל דנון <danondaniel@gmail.com> wrote: > Sorry for the double-post, forgot to add up the way I thought about using: > > Simple sql query: > > SELECT * FROM users as u  WHERE (SELECT COUNT(id) FROM notes > WHERE user_id > = u.id LIMIT 0,1) = 0 > > Problem is I have about 450,000 "users" and about 90% don't have > "notes", > and it takes LOADS of times even with I limit it: > > SELECT * FROM users as u  WHERE (SELECT COUNT(id) FROM notes > WHERE user_id > = u.id LIMIT 0,1) = 0 LIMIT 0,10 > > Takes about 10 seconds which is too much time... Any way to optimize it? > > On Sun, Dec 20, 2009 at 11:30 PM, דניאל דנון <danondaniel@gmail.com> wrote: > >> Hey, Lets assume I got a table named "users". >> It contains id & name. >> >> I have another table called "notes" - which contains id, user_id, contents >> >> >> I want to delete all users from table "users" that don't have notes (SELECT >> ... FROM notes WHERE user_id=ID) returns empty result. >> >> >> What is the fastest way to do it? >> >> -- >> Use ROT26 for best security >> > > > > -- > Use ROT26 for best security >