I would go with join rather than where condition. 2011/4/26 Halász Sándor <h...@tbbs.net>
> >>>> 2011/04/25 17:42 +0300, Andre Polykanine >>>> > Here is the first one. > We have two queries: > SELECT `blogs`.* FROM `Blogs` LEFT JOIN `Users` ON > `Blogs`.`UserId`=`Users`.`Id`; > and the following one: > SELECT `Blogs`.* FROM `Blogs`, `Users` WHERE > `Blogs`.`UserId`=`Users`.`Id`; > > 1. Are they identical? > 2. Which is better (faster, more optimal, more kosher, I mean, better > style...)? > <<<<<<<< > > >>>> 2011/04/25 10:16 -0500, Johnny Withers >>>> > The only difference once MySQL parses these two queries is the first one is > a LEFT JOIN, which will produce all records from the blogs table even if > there is no matching record in the users table. The second query produces > an > INNER JOIN which means only rows with matching records in both tables will > be returned. > > ... > > I prefer to write the INNER JOIN out though because it leaves my WHERE > clause to do filtering. > <<<<<<<< > and it is usual to write all about the joining in the FROM-clause --the > tables and the criterion for joining them-- and reserve the WHERE-clause for > filtering the result: > > SELECT `blogs`.* FROM `Blogs` LEFT JOIN `Users` ON `Blogs`.`UserId` = > `Users`.`Id` > > SELECT `Blogs`.* FROM `Blogs` JOIN `Users` ON `Blogs`.`UserId` = > `Users`.`Id` > > That is, if you already had a table with the joined outcome, you would use > the WHERE-clause to determine what of it enters into further processing. > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/mysql?unsub=sureshkumar...@gmail.com > > -- Thanks Suresh Kuna MySQL DBA
