Night Dreaming (by Sudar)

During my days with dreamhost, in order to access MySQL from my local machine, I used to add my ip to the allowed host list. Even though security is compromised here, I really liked to use HeidiSQL for accessing MySQL database server instead of the built in MySQL console. But after my move to SliceHost, I found a little trick using which I can continue to use HeidiSQL from my local machine without adding my ip to the allowed host list.

This nice little trick is called port forwarding. Let me show you how I configured PuTTY so as to enable port forwarding.
First install MySQL and then configure SSH to use key based authentication and change the default port by following the articles at Slicehost. After installing MySQL and configuring SSH, download and install PuTTY from its download page. I recommend you to download the zip file containing all the files.

Then create a new session in PuTTY by entering the ip address and also the port. Then choose Connection -> SSH -> Tunnels. In the source port field enter a valid port number like 8600. In the destination field enter the value 127.0.0.1:3306. 3306 is the default port in which MySQL runs. The reason why I asked you to enter a different port in the source is that, in future if you run a MySQL server in your local machine for testing, it will clash with your port forwarding. Click the Add button and then start the session. Don’t forget to save the session.

Now open your favourite MySQL GUI client. Mine is HeidiSQL. In the connection settings, enter 127.0.0.1 as the Hostname and enter the port which you specified in the source field in PuTTY (8600) as port. Also enter your username, password, default database name and the click connect.

Now the request which goes to port 8600 of your local machine is forwarded to port 3600 of your MySQL server by PuTTY and you can safely use a GUI client for MySQL without adding any ip to the allowed host list. Note that it will work only when PuTTY is having the session opened.

I hope this is of help to you and let me know how it is working for you. Happy PuTTYing

Tags: HeidiSQL, Linux/Unix, MySQL, PuTTY, slicehost, SSH

Recently I moved my WordPress blog to a new server. I took the dump of the old database and imported it into the new MySQL server. Everything was fine except that I stated getting some strange characters in my posts. For instance I was getting (Nov — 3rd — 2007) instead of (Nov - 3rd - 2007).

It took me lot of research and googling to find the solution and so I thought of sharing it here so that it would be helpful for others who might face the same problem.

First I raised a support request in WordPress, but didn’t get a reply. After some googling, I found that it was due to wrong character set in my new MySQL server. Instead of having utf8 as the character set the MySQL database server was running in the default latin1 character set.

I changed the character set in the MySQL my.conf file and also in the wp-config.php file of WordPress and re imported the tables. Even this didn’t solve my problem. Later I found that there were certain characters in my wp-posts table which were encoded in latin1 character set even though the table is set to utf8 character set.

I then exported the table using a tool called Heidisql (which is by the way an excellent alternative to the command line MySQL client). I then opened the sql file in a text editor and changed all instances of latin1 to utf8 (basically a find/replace). I saved the file and imported the tables again and the junk characters are gone.

So the lesson learned the harder way, KEEP EVERYTHING IN UTF-8, ABSOLUTELY EVERYWHERE, FROM DAY ONE. You’ll be glad you did some day.

Tags: Character, MySQL, set, utf8, WordPress

One of my colleagues showed me this gem in Oracle and I thought of documenting it here so that it will be useful for everyone and also I can find it next time I need it by just searching my blog instead of Google. Using this query you can find out the start time of the Oracle database server.

SELECT * FROM V$INSTANCE

In addition to the start time the query also returns other useful information like instance name, version, hostname etc. The hostname is particularly useful when TNSNAMES.ORA is playing tricks with you.

Tags: Oracle, Query

A friend of mine recently asked me how to select random rows from a table using a SQL query which let me to find a solution. If you are wondering why we need to select rows randomly from a table, consider a simple example of an online quiz which needs to display the questions in a random order for each person who is going to take the exam.

After a bit of research and googling I found the answer and then thought of sharing it here so that I can refer it at a later point of time and at the same time it may be useful for others who are searching for a similar solution.

In Oracle we have to use the sys_guid() function. The query will look like

SELECT col1, col2 FROM tblname ORDER BY SYS_GUID()

In SQL Server the query would look like

SELECT col1, col2 FROM tblname ORDER BY NEWID()

In MySQL the query would look like (Thanks Aswin)

SELECT col1, col2 FROM tblname ORDER BY RAND()

If any of you know how to do this in other databases or have a better solution than this, leave it the comments so that I can mention them here.

Tags: newid, SQL, sys_guid

I came across a unique requirement at work for which I struggled a lot to write the SQL query. Then after some googling and tips from my DBA friends I finally came up with the query. I never came across this query before, so I thought of posting about it here, since some of you might benefit from it.

Since I cannot tell you the exact requirement or the table structure I mapped it with the classic emp table to illustrate the query.

Ok so consider the following table structure

SEQ_ID - unique sequence number
EMP_ID - unique emp id
DEP_ID - department id (from a master table)
SAL - salary


And now the requirement is to find the employee with the max salary in each department.

The query

SELECT dep_id, MAX(sal) FROM tbl_name GROUP BY dep_id

will give me the maximum salary in each department, but now the real problem is to find out the person with that maximum salary in each department.

So finally I came up with this query

SELECT * FROM tbl_name WHERE (dept_id, sal) IN (SELECT dep_id, MAX(sal) FROM tbl_name GROUP BY dept_id)

The reason why I found this syntax to be strange for me is that I have never used two parameters in the IN clause.

The above query works, (atleast for me in Oracle 9i) but I am not sure whether it is the most optimal way of doing it. So if any of you know a better solution then do let me know.

Tags: Oracle, self-join, SQL, subquery

I found SQLyog GUI - MySQL Front end tool while searching for a replacement for phpMyAdmin. Really cool… It is similar to Query Analyser which comes with SQL Server. Just now installed it and playing around it.

Tags: phpMyAdmin, SQLyog

‘Out of all the replication procedures available for SQL Server Merge Replication is the most difficult one to implement’. I had this thought till i found this article. This step-by-step guide clearly explains how to Setup up a Merge Replication. Check it out.

Tags: Merge, Replication, SQLServer

Check out NGS Software SQLCrack

NGSSQLCrack is an innovative password cracking utility for Microsoft SQL Server 7 and 2000 that can assist enterprises in securing their infrastructures. NGSSQLCrack allows system administrators and security professionals to quickly scan systems for weak passwords that are susceptible to brute force attack, and guard against them. An handy tool if you are worried about the security in your network.

Check it out for yourself

Tags: Cracking, Password, SQLServer

Check out this excellent article Images and SQL Server from SQL Team.

This article tells you how to store and retrieve images in a SQL Server. Really good one.

Tags: Images, SQLServer

Have you ever wondered how to estimate the size of the SQL Server’s table? Then this artilce from MSDN might be very useful.

Check out Estimating the Size of a Table article

This will really handy in lot of situations.

Tags: Article, SQLServer