Emulate auto-increment in MySQL/InnoDB

Question

Assume I am going to emulate auto-increment in MySQL/InnoDB

Conditions

1. Using MySQL/InnoDB
2. The ID field don\'t have unique index, nor it is a PK

Answer 1

Create another table with a single row and column that stores the next id value. Then create an insert trigger on the original table that increments the value in the second table, grabs it, and uses that for the ID column on the first table. You would need to be careful with the way you do the select and update to ensure they are atomic.

Essentially you are emulating an Oracle sequence in MySQL. It would cause a lock on single row in the sequence table though, so that may make it inappropriate for what you are doing.

ETA:

Another similar but maybe better performing option would be to create a second "sequence" table that just has a single auto-increment PK column and no other data. Have your insert trigger insert a row into that table and use the generated ID from there to populate the ID in the original table. Then either have the trigger or another process periodically delete all the rows from the sequence table to clean it up.