Archive for December, 2009

A useful command for mac os x terminal

When working on your server with ssh access, you tend to get very used to doing everything you need to do via the terminal window. Sometimes you may come accross problems which unless you have the know how you will be puzzled as to why somethings not working.

Today I came across a small problem in that a few commands which would normally work on my local os x machine were not working on my server machine.
Im going to use the ‘zip’ function as my guinea pig. If this function is not installed or enabled in your servers configuration/installation you will see a message like this:

-bash: zip: command not found

This is easy to fix simply by running the following command:

yum install zip

Now if you try the zip command again you will notice its worked or at least should work. You can also if you wish check to see if its installed first by viewing the install list on your server with the following command.

rpm -qa

How to find duplicate rows of a table in sql

This is a nice quick easy way to find duplicate rows in your database based on one field.
So say for instance id like to find all users with duplicate rows in my orders table.

The following query can achieve that.

select userid, count(*) from orders group by userid HAVING count(*) > 1

//this will fetch all the userids with duplicate rows, then you could run a delete query or whatever it is you need to do to get rid of them in a while loop of this.