http://dev.mysql.com/doc/refman/5.0/en/internal-locking.html
The following is the extract from the documentation.
mysql> LOCK TABLES real_table WR
how will I know that some tables are locked?
You can use SHOW OPEN TABLES command to view locked tables.
how do I unlock tables manually?
If you know the session ID that locked tables - 'SELECT CONNECTION_ID()', then you can run KILL command to terminate session and unlock tables.
With Sequel Pro:
Restarting the app unlocked my tables. It resets the session connection.
NOTE: I was doing this for a site on my local machine.
Here's what i do to FORCE UNLOCK FOR some locked tables in MySQL
1) Enter MySQL
mysql -u your_user -p
2) Let's see the list of locked tables
mysql> show open tables where in_use>0;
3) Let's see the list of the current processes, one of them is locking your table(s)
mysql> show processlist;
4) Let's kill one of these processes
mysql> kill put_process_id_here;