Mysql – How to find the difference between queries that return multiple rows

OMG !!! Look at the output of df -h

Size: 20G Used: 19G Available 0 Use Percent: 100%

YOU HAVE NO DISK SPACE !!!

Get more diskspace freed up or have linode increase diskspace.

According to MySQL 5.0 Certification Study Guide

Page 408,409 Section 29.2 Bulletpoint 11 says:

If you run out of disk space while adding rows to a MyISAM table, no error occurs. The server suspends the operation until space becomes available, and then completes the operation.

In reality, mysqld is not dead. It is waiting for free diskspace to continue whatever it normally does. Even during startup, if mysqld makes a temp table, it is a MyISAM table. No space left on the disk? No problem. MyISAM just patiently waits for you to make free space.

If you have an error file like /var/log/mysql/log, clear its contents like this:

echo -n > /var/log/mysqld.log

If the error file in /var/lib/mysql/my-machine.err then do this:

echo -n > /var/lib/mysql/my-machine.err

Give it a Try !!!

The simplest structure would be a PERMISSIONS table like this:

create table PERMISSIONS
( Site_ID int
, User_ID int
, Role char(1)
, primary key (Site_ID, User_ID, Role) -- scenario 1
-- OR:
, primary key (Site_ID, User_ID) -- scenario 2
) 

Use values for Role such as:

• A = Administrator
• P = Publisher
• E = Editor

How many rows you need depends on how your code interprets the data. You could have very simple code which interprets each permission strictly at face value. To do an administrative task, the user would need an 'A' permission. To do a publishing task, they would need a 'P' permission, etc. In this case an administrator would need three records per site (one each of A, P, E). Similarly publishers would need two records per site and editors only one. There is a risk in this approach that data consistency errors could creep in, like someone could be a publisher, but not an editor (by virtue of the 'E' record being missing).

Alternatively, you could make your code more complex, in which case each user only needs one permission record per site. In this scenario, administrative tasks require an 'A' permission, publishing requires an 'A' or a 'P' and editing requires 'A', 'P', or 'E'. The advantage of this approach is that there is less data to maintain and you won't have inconsistencies.

Note too that you do not need to have the Users.Parent column. If an administrator has an 'A' permission for a site, that automatically gives them control of all of the users for that site.