fenway

First, you probably don't need to case all of those -- mysql deals with datetime<=>date conversions quite well. Second, what are you trying to achieve?

There is a FLUSH TABLES command, but I doubt that's the issue.

Tuples in the DB?

You sure mysql is correctly configured?

Please don't use TEXT.... it's horrible... if you're using mysql5, varchar goes up to 65k.

An example of the insert statement and the table definition would help, too.

Yes, that is the hard way... usually, you get the most recent for each one, then join that table back.

Yes, be very careful about this!

Why not use SUM( IF( yourfield between x and y), 1, 0) multiple times?

That's wrong... you want CURDATE() - INTERVAL 7 DAY

It seems to be joining the tables the wrong way... use straight join, or try running analyze.

Which query is the problem?

I'm not sure sure what you mean...

Try: select s.*, c.* from classes as c inner join students on c on c.id. = s.classes_id

You're missing a limit clause.

Too little info to answer your question.

Hopefully this presentation will stay online at scribd... it's simply fantastic, probably the best I've come across in recent memory. At 220 slides, it's quite lengthy -- but the lessons learned are invaluable, so be sure to read all the way to the end. A MUST READ!!!! EDIT: This year's version of the presentation -- some really great stuff in here, particuarly about hierarchies.

At the 2008 MySQL Conference and Expo, The Pythian Group gave away EXPLAIN cheatsheets (PDF).

This resource covers a very broad range of topics... it's worth a look, though, especially if you're stumbling in the early stages of configuration.

Basically, this blog contains a regularly-updated run-down of MySQL functions, with a short description and a few hints on how to use them; RSS feed here.

Please read the excellent FAQ thread on this issue by our very own wildteen88.

To ensure that your post gets answered as soon as possible, please make sure you've included the following: your MySQL server version -- absolutely required! the raw MySQL statement in question [in a CODE block, and without any PHP variables] any errors that MySQL returns to the client [from mysql_error()] the table structure & column indexes of the relevant tables [via SHOW CREATE TABLE is preferred] the EXPLAIN output for your query, if applicable a clear and concise description of what you want this statement to achieve a description of what it's currently doing that's not to your liking a brief listing of the types of things you've attempted so far If you don't provide any or all of the above, don't be surprised if your post never gets the attention it deserves. --fenway

You'll find a very good list of do's and don'ts written by Matt Kruse here -- highly recommended.

MySQL's tech resource article on database normal forms is an excellent read. NEW!!! - A large (160MB, 4M record) sample database with test suite for MySQL -- fantastic for running "real" queries. In addition, MySQL provides a number of sample databases for testing purposes; personally, I find this one to be the most useful for playing around with SQL statements and such. The Zip Code Database Project exists to provide US Zip Codes in their entirety; latitude and longitude coordinates included! The downloads are in CSV and MySQL table dump formats. Also, there's an pretty good online "data generator", and SQL is one of the options... although personally, I prefer the integers table approach (courtesy of Baron Schwartz): set @num_gamers := 10000, @num_countries := 5, @num_games := 10; drop table if exists gamer; drop table if exists game; drop table if exists country; drop table if exists score; drop table if exists semaphore; create table gamer( gamer int not null, country int not null, name varchar(20) not null, primary key(gamer) ); create table game( game int not null, name varchar(20) not null, primary key(game) ); create table score( gamer int not null, game int not null, score int not null, primary key(gamer, game), index(game, score), index(score) ); create table country( country int not null, name varchar(20) not null, primary key(country) ); -- I use the integers table to generate large result sets. drop table if exists integers; create table integers(i int not null primary key); insert into integers(i) values(0),(1),(2),(3),(4),(5),(6),(7),(,(9); insert into country(country, name) select t.i * 10 + u.i, concat('country', t.i * 10 + u.i) from integers as u cross join integers as t where t.i * 10 + u.i < @num_countries; insert into game(game, name) select t.i * 10 + u.i, concat('game', t.i * 10 + u.i) from integers as u cross join integers as t where t.i * 10 + u.i < @num_games; insert into gamer(gamer, name, country) select th.i * 1000 + h.i * 100 + t.i * 10 + u.i, concat('gamer', th.i * 1000 + h.i * 100 + t.i * 10 + u.i), floor(rand() * @num_countries) from integers as u cross join integers as t cross join integers as h cross join integers as th; insert into score(gamer, game, score) select gamer.gamer, game.game, floor(rand() * @num_gamers * 10) from gamer cross join game;

This page contains some in-depth, extremely well-written articles on query optimization in very common situations. A collection of fantastic resources on the subject of MySQL Performance: A Few Common Performance Mistakes - NEW! Join-fu: The Art of SQL Tuning - NEW! Basic Performance Tuning of SQL Queries and Schema/Index Strategies (FAQ) MySQL Performance Tuning - Best Practices MySQL Index Tuning and Coding Techniques for Optimal Performance MySQL Server Variables MySQL Server Variables - SQL layer or Storage Engine specific Optimizing Rank Data in MySQL Group-Wise Maximum -- doesn't really belong here, but it's an important concept anyway