How do I enable the MySQL slow query log?

My MySQL version details are

1. Server: Localhost via UNIX socket
2. Software: MySQL
3. Software version: 5.0.96-community-log - MySQL Community Edition (GPL)
4. Protocol version: 10

How do I enable the MySQL slow query log?

Version 5.1.6 and above:

1. Enter the MySQL shell and run the following command:

set global slow_query_log = 'ON';

2. Enable any other desired options. Here are some common examples:

Log details for queries expected to retrieve all rows instead of using an index:

   set global log_queries_not_using_indexes = 'ON'

Set the path to the slow query log:

  set global slow_query_log_file ='/var/log/mysql/slow-query.log';

Set the amount of time a query needs to run before being logged:

   set global long_query_time = 20;
     (default is 10 seconds)

3. Confirm the changes are active by entering the MySQL shell and running the following command:

show variables like '%slow%';

Versions below 5.1.6:

1. Edit the /etc/my.cnf file with your favorite text editor vi /etc/my.cnf

2. Add the following line under the “[mysqld]” section. Feel free to update the path to the log file to whatever you want:

   log-slow-queries=/var/log/mysql/slow-query.log

3. Enable additional options as needed. Here are the same commonly used examples from above:

Set the amount of time a query needs to run before being logged:

  `long_query_time=20
  (default is 10 seconds)`

Log details for queries expected to retrieve all rows instead of using an index:

 `log-queries-not-using-indexes`

4. Restart the MySQL service:

service mysqld restart

5. Confirm the change is active by entering the MySQL shell and running the following:

show variables like '%slow%';

Update:1

According to MySQL docs, the error #1193 occurs when you use wrong code for SQLSTATE.

Message: Unknown system variable %s

And, as you can see on the same page, the SQLSTATE 99003 is not defined.

refer this link:

http://dev.mysql.com/doc/refman/5.5/en/slow-query-log.html

http://dev.mysql.com/doc/refman/5.1/en/slow-query-log.html

If your server is above 5.1.6 you can set the slow query log in the runtime itself. For which you have to execute this queries.

set global log_slow_queries = 1;
set global slow_query_log_file = <some file name>;

Or alternatively you can set the this options in the my.cnf/my.ini option files

log_slow_queries = 1; 
slow_query_log_file = <some file name>;

Refer: http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_slow_query_log_file