SELECT * FROM t1 AS t
WHERE 2 = (SELECT COUNT(*) FROM t1 WHERE t1.id = t.id);
Find a value appears twice in a table
March 8th, 2011Clear Facebook Cache
February 28th, 2011http://developers.facebook.com/tools/lint
How to customize Facebook Link Sharing
February 28th, 2011Put the following metatag in the html header of the sharing page. FB will pick this up automatically.
Customize logo
Customize Title
Customize Description
Cannot delete or update a parent row: a foreign key constraint fail
December 25th, 2010To delete a table that has a foreign key constraint, you will get the following error.
Cannot delete or update a parent row: a foreign key constraint fail
You can temporarily disable the foreign key referential check by the following command.
SET foreign_key_checks = 0;
drop table xxx;
SET foreign_key_checks = 1;
Shorten the URL for Gmail Hosting Services
October 13th, 2010there is a way to shorten the url for gmail hosting services, all you have to do is to create a CNAME record in your DNS Server.
For example, this is the long URL to access to the gmail hosting service.
https://google.com/a/mydomain.com
Create a CNAME record in your DNS server.
mail IN CNAME ghs.google.com.
then when you type
http://mail.mydomain.com
it will redirect to your gmail hosting url
https://google.com/a/mydomain.com
Multiple Smart Relay for Exchange 2007 SBS
October 7th, 2010The default SBS Console only allows you to add 1 Smart Relay to deliver email. If you need to setup multiple smart relay host – you will need to set it up from the Exchange Management Console
– Start up your Exchange Management Console
– Under Organization Configuration -> Hub Transport -> Send Connectors
– Click Properties
– Under Network
– ADD / DELETE the smarthost from there
Search and Replace in VI
September 18th, 2010To Search and Replace in VI.
:%s/search_string/replacement_string/g
% is equal to all lines in a file
g is equal to global. Replace all occurrence of the search result.
Install Mac Mini Server without a DVD ROM Remotely
August 29th, 2010There is a number of ways to install a Mac Mini Server Remotely. I found the following way seems to be the easiest among the others.
Pre-requistics:
1. you have a Mac Mini Server connected to a Network (preferably over Gigabit Ethernet)
2. you have a Mac Book connected to a the same Network with the Mac Mini Server (preferably over Gigabit Ethernet)
Procedures:
1. Insert the Installation DVD onto the Mac Book.
2. on your Mac Book, Open the HDD > Applications > Utilities, Start Remote Install Mac OS X
3. Press and Hold the “OPTION” key (or “ALT” on a PC Keyboard) on the Mac Mini Server and turn on the power
4. Select the Target Installation Disc to start up the computer
Enable Error Reporting for PHP
August 5th, 2010If you don’t have access to the php.ini or have issue setting up .htaccess to enable error reporting.
You can try the following code
ini_set( ‘display_errors’, true );
error_reporting( E_ALL );
Finding out the process is occupying the Network Port on Windows and Linux
August 3rd, 2010You ever have a problem trying to start an application and it failed to start because the network port was occupied by another application? To find out the application that using the port is painstaking. The following commands could help you.
In the following example, I am trying to find what is the process that is occupying the port 8080.
Windows
C:\Documents and Settings\terence>netstat -aon | findstr 8080
TCP 0.0.0.0:8080 0.0.0.0:0 LISTENING 1748C:\Documents and Settings\terence>tasklist | findstr 1748
TNSLSNR.EXE 1748 Console 0 6,264 K
Linux
[root@mail03a ~]# netstat -nap | grep 8080 | grep LISTEN
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 2685/openvpn