如何在不牺牲完整性的情况下在MySQL数据库表中获取最新的设置ID？

Question

I'm using PHP to insert groups of records into a MySQL DB.
Whenever I insert a group of records, I want to give that group a unique set ID that is incremented by 1 for each group of records in the DB.

Currently, I'm checking the latest set ID in the DB and incrementing it by 1 for each new set of records.
The thing that scares me though is what happens if I query the DB to get the latest set ID, and before I can insert a new set of records with that set ID + 1, another insert occurs on the table thus taking the set ID I was about to use?
While fairly unlikely, something like that could greatly sacrifice the integrity of the data.

What can I do to prevent such a thing from happening? Is there any way to temporarily lock the DB table so that no other inserts can occur until I have performed a SELECT/INSERT combo?

Answer 1

Locking the table is one option, but that approach impacts concurrency.

The approach I would recommend is that you use a separate table with AUTO_INCREMENT column, and use a separate INSERT into that table, and a SELECT LAST_INSERT_ID() to retrieve the auto_increment value.

And then use that value as the group identifier for the group of rows you insert into your original table.

Answer 2

The basic approach is:

LOCK TABLE foo WRITE;
SELECT MAX(id) + 1 FROM foo
INSERT ...
INSERT ...
UNLOCK TABLES;

Locking the table prevents any other process from changing the table until you explicitly unlock it.

Having said that, seriously consider just using a table with an AUTO_INCREMENT column. MySQL will do the work of maintaining unique keys wholly automatically, and then you can simply refer to those keys from your existing table.