HeatWare.net » Databases

How to delete/drop a constraint in PostgresSQL

sood — Thu, 18 Jun 2009 18:51:57 +0000

This article will show you how to drop a contraint, such as a foreign key contraint, on a PostgresSQL 8.x database.

psql -U [username] [database_name]

Show a list of constraints on a particular table

\d [table_name]

To Delete (or Drop) the constraint, use the command:

ALTER TABLE [table_name] DROP CONSTRAINT [constraint_name];

How to parse a decimal number using ‘awk’ and ‘cut’ in Linux

sood — Thu, 02 Apr 2009 20:12:36 +0000

This article will show you how to parse a decimal number (such as a software release number) into individual parts. For example, you can do this if you need to compare the the minor release number of two versions. There are numerous ways to accomplish the same thing using Linux and I will show you two of them: awk and cut.

Example 1 – Using awk

Number: 52.4

echo "52.4" | awk 'BEGIN {FS="."}{print $1, $2}'
Output: 52 4

echo "52.4" | awk 'BEGIN {FS="."}{print $1}'
Output: 52

echo "52.4" | awk 'BEGIN {FS="."}{print $2}'
Output: 4

Example 2 – Using cut

Number: 1.0.2.66

echo "1.0.2.66" | cut -d. -f1
Output: 52 4

echo "1.0.2.66" | cut -d. -f2
Output: 0

echo "1.0.2.66" | cut -d. -f3
Output: 2

echo "1.0.2.66" | cut -d. -f4
Output: 66

There you have it, two different methods for parsing decimal numbers!

How to install a FTP server on Linux in 30 seconds

sood — Wed, 25 Feb 2009 18:11:44 +0000

This article will show you how to install a FTP server (vsftpd) on Linux in under 30 seconds.

Installing a FTP Server on Linux

yum -y install vsftpd

After the installation is complete, you must start the FTP server by running the command:
service start vsftpd

Thats all there is to it! A couple things to note:

The default username and password is anonymous
The default home directory is /var/ftp/
The default port number is 21
You must have your firewall disabled on port 21 in order to accept outside connections

Troubleshooting

If you are unable to connect to the FTP server from a remote computer, be sure to disable the firewall on port 21. If you Linux distribution uses iptables to manage the firewall, use the following command:

iptables -I RH-Firewall-1-INPUT -s 0.0.0.0/0 -p tcp -d 0.0.0.0/0 --dport 21 -m state --state NEW -j ACCEPT

How to install,upgrade, and uninstall a Linux RPM package

sood — Tue, 17 Feb 2009 17:35:11 +0000

This article will show you to how install,upgrade, and uninstall a RPM package on Linux. For additional RPM commands such as listing all installed RPMs on the box and detailed package information such as version, date created, file listing, etc. check out How to Find All Installed RPMs in Linux.

To install a RPM

rpm -ivh [package name]

To upgrade a RPM

rpm -Uvh [package name]

To uninstall a RPM

First find the exact package name by issuing the following command:
rpm -qa | grep -i [search string]

Then begin the uninstall process by running:
rpm -Uvh [package name]

Find PostgreSQL database size using SQL ‘Select’

sood — Wed, 07 Jan 2009 16:06:38 +0000

This article will show you a very simple way to find the size of a PostgreSQL database using a SQL SELECT statement. This will work on PostgreSQL version 8.3.3, but should work on older versions as well.

Query

SELECT pg_database.datname,pg_size_pretty(pg_database_size(pg_database.datname)) AS size FROM pg_database where datname='database_name';

Sample Result

datname | size -----------------+------- database_name | 15 MB (1 row)

The result shows the name of the database, as well as the size which in this case is 15 MB