Basic join query understanding

Posted by OM The Eternity on Stack Overflow See other posts from Stack Overflow or by OM The Eternity
Published on 2010-05-10T05:59:03Z Indexed on 2010/05/10 6:04 UTC
Read the original article Hit count: 376

Filed under:

mysql

|

left-join

|

join

I know this very silly, but can anybody help me in understanding what does this join query is doing in elabortive description?

SELECT j1.* FROM jos_audittrail j1 LEFT OUTER JOIN jos_audittrail j2  ON (j1.trackid = j2.trackid AND j1.field = j2.field 
  AND j1.changedone < j2.changedone)
 WHERE j1.operation = 'UPDATE'  AND j1.trackid=$t_ids[$n] AND j2.id IS NULL

I know its very silly, but i need to go ahead with my further need... Pls do help me...

© Stack Overflow or respective owner

Related posts about mysql

How to remove MySQL completely with config and library files on ubuntu 12.04 gnome 3.0

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I tried everything till now: sudo apt-get remove mysql-server mysql-client mysql-common sudo apt-get purge mysql-server mysql-client mysql-common sudo apt-get autoremove and even more commands... But whenever I am trying to locate mysql. I get a no. of files related to mysql command: shell>>… >>> More
mysql: Cannot load from mysql.proc. The table is probably corrupted

as seen on Server Fault - Search for 'Server Fault'
Mysql was started: /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 but when I'm trying to do something: ERROR 1548 (HY000) at line 1: Cannot… >>> More
mysql: Bind on unix socket: Permission denied

as seen on Server Fault - Search for 'Server Fault'
Can't start mysql with: sudo /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 120222 13:40:48 mysqld_safe Starting mysqld daemon with databases… >>> More
Why is there a /etc/init.d/mysql file on this Slackware machine? How could it have gotten there?

as seen on Server Fault - Search for 'Server Fault'
A client of my IT-consulting service owns a web-development shop. He's been having problems with a Slackware 12.0 server running MySQL 5.0.67. The machine was set up by the client's sysadmin, who left on bad terms. My client no longer employs a sysadmin. As far as I can tell, the only copy of MySQL… >>> More
MySQL – Learning MySQL Online in 6 Hours – MySQL Fundamentals in 320 Minutes

as seen on SQL Authority - Search for 'SQL Authority'
MySQL is one of the most popular database language and I have been recently working with it a lot. Data have no barrier and every database have their own place. I have been working with MySQL for quite a while and just like SQL Server, I often find lots of people asking me if I have a tutorial which… >>> More

Related posts about left-join

Select query 2-3 times faster than view

as seen on Stack Overflow - Search for 'Stack Overflow'
This query run alone: SELECT -- lots of columns FROM (((((((((((`table1` `t1` LEFT JOIN `table2` `t2` ON(( `t2`.`userid` = `t1`.`userid` ))) LEFT JOIN `table3` `t3` ON(( `t1`.`orderid` = `t3`.`orderid` ))) … >>> More
Mysql - Help me change this single complex query to use temporary tables

as seen on Stack Overflow - Search for 'Stack Overflow'
About the system: - There are tutors who create classes and packs - A tags based search approach is being followed.Tag relations are created when new tutors register and when tutors create packs (this makes tutors and packs searcheable). For details please check the section How tags work in this system… >>> More
Left Join in Subsonic3

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi there, I'm new in subsonic3, and I'm getting some errors when I try to use LeftJoin var q = from c in categories join p in products on c equals p.Category into ps from p in ps.DefaultIfEmpty() select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName… >>> More
SQL is this equvelent to a LEFT JoIn?

as seen on Stack Overflow - Search for 'Stack Overflow'
Is this equvelent to a LEFT JOIN? select distinct a.name, b.name from tableA a, (select name from tableB) as b It seems as though there is no link between the two tables. Is there an easier / more efficient way to write this? >>> More
Another rookie question; How to implement Count() here?

as seen on Stack Overflow - Search for 'Stack Overflow'
I have this query: SELECT mt.*, fordon.*, boende.*, elektronik.*, business.*, hem_inredning.*, hobby.* FROM classified mt LEFT JOIN fordon ON fordon.classified_id = mt.classified_id LEFT JOIN boende ON boende.classified_id = mt.classified_id LEFT JOIN elektronik ON elektronik.classified_id = mt… >>> More