Terence <[EMAIL PROTECTED]> wrote on 11/23/2005 08:22:30 PM:
> Hi All,
>
> We have upgraded from 4.1.0 to 5.0.16 and notice all left joins not
> working. It works fine on 4.1 but 5.0.16 gives us an error:
>
>
> How to reproduce:
>
> CREATE TABLE `user_master` (
> `user_id` int(5) unsigned NOT NULL auto_increment,
> `department_id` int(5) default NULL,
> `role_id` int(5) unsigned default NULL,
> `username` varchar(50) NOT NULL,
> PRIMARY KEY (`user_id`),
> UNIQUE KEY `user_id` (`user_id`),
> KEY `user_id_2` (`user_id`)
> );
>
> CREATE TABLE `role_master` (
> `role_id` int(5) unsigned NOT NULL auto_increment,
> `role_name` varchar(50) NOT NULL,
> PRIMARY KEY (`role_id`),
> UNIQUE KEY `role_id` (`role_id`),
> KEY `role_id_2` (`role_id`)
> );
>
>
> CREATE TABLE `department_master` (
> `department_id` int(5) unsigned NOT NULL auto_increment,
> `department_name` varchar(50) NOT NULL,
> PRIMARY KEY (`department_id`),
> UNIQUE KEY `department_id` (`department_id`),
> KEY `department_id_2` (`department_id`)
> );
>
>
> INSERT INTO role_master(role_name) VALUES('Administrator');
> INSERT INTO department_master(department_name) VALUES('ITS');
> INSERT INTO user_master(department_id,role_id,username)
> VALUES('1','1','Joey');
>
> SELECT um.username,rm.role_name,dm.department_name
> FROM user_master um, role_master rm
> LEFT JOIN department_master dm ON um.department_id = dm.department_id
> WHERE um.role_id = rm.role_id;
>
>
> 1054 - Unknown column 'um.department_id' in 'on clause'
> Query:
> SELECT um.username,rm.role_name,dm.department_name
> FROM user_master um, role_master rm
> LEFT JOIN department_master dm ON um.department_id = dm.department_id
> WHERE um.role_id = rm.role_id
> =====
>
>
> Has the left join syntax changed?
>
> --
> Terence Le Grange
> Senior IS Executive - ITS
> Sunway University College
> Email: [EMAIL PROTECTED]
> Phone: (+603) 7491 8623 ext. 8078
> Website: http://www.sunway.edu.my
>
The SQL didn't change, the query engine was debugged. That is the error
you should have been getting all along but weren't. Please check the
manual for a full explanation but the short version is that crappy
comma-delimited method of making a CROSS JOIN has been demoted in
evaluation priority (where it should be). Three options:
a) swap the order you list the tables so that user_master appears next to
the LEFT JOIN
b) use parentheses to reprioritize the joins so that user_master CROSS
JOINs to role_master BEFORE you LEFT JOIN to department_master
c) quit using the comma. Use CROSS JOIN instead.
Shawn Green
Database Administrator
Unimin Corporation - Spruce Pine
