How to lock records in a table?

While there shouldn't be many reasons to do this in MGA database system like Firebird, there are ways to do it.

One is to use a dummy update for all the records you wish to lock. Many developers do this by accident and get the deadlocks. Example that locks employee 8:

-- start transaction
update employee set emp_no = emp_no where emp_no = 8;
update employee set ... where emp_no = 8;
-- end transaction

A more elegant way is to use the SELECT ... WITH LOCK syntax.

-- start transaction
select * from employee where emp_no = 8 WITH LOCK;
update employee set ... where emp_no = 8;
-- end transaction

Please note that locking easily leads to deadlocks with NO WAIT and application hanging with WAIT transactions. Use it only if you're really sure you know what you are doing and why.

Do you find this FAQ incorrect or incomplete? Please e-mail us what needs to be changed. To ensure quality, each change is checked by our editors (and often tested on live Firebird databases), before it enters the main FAQ database. If you desire so, the changes will be credited to your name. To learn more, visit our add content page.

All contents are copyright © 2007-2023 unless otherwise stated in the text.

Links   Firebird   News   FlameRobin   Powered by FB: Home Inventory   Euchre  
Add content   About  

 Installation and setup
 Backup and restore
 Connectivity and API
 Errors and error codes