Question

I have 3 options of adding a new UNIQUE id (primary_key) to one of my particular tables.

1. Create AUTO_INCREMENT field.
2. SELECT id FROM table ORDER BY id DESC LIMIT 1
3. SELECT MAX(id) FROM table

I’m currently using option 2, as people might delete rows from the table they access, so id’s get freed, otherwise i’d be using option 1

What do you reccommend ?

Answer 1

You should always use option 1 (in order to avoid the race hazard of two simultaneous inserting clients reading the current maximum id before either has completed their insertion). AUTO_INCREMENT prevents this hazard from occurring through the use of locks that make the read & write operations atomic.