I've come across this problem numerous times but haven't found a "MySQL way" to solve the issue as such - I have a database that contains users and reports. Each report has an id which I display as a report number to my users.
The main complaint is that users are confused as to why reports have gone missing from their system. This is not actually the case. It is actually that they are recognizing a gap between their IDs and assume that these are missing reports, when in actual fact, it is simply becasue another user has filled in this auto-incrementing gap.
I need to know if there is a way to do this in MySQL:
Is it possible that I can have a second auto-increment field called report_number which is based on a user_id field which has a different set of auto-increments per user?
e.g.
|------|---------|---------------|
| id | user_id | report_number |
|------|---------|---------------|
| 1 | 1 | 1 |
| 2 | 1 | 2 |
| 3 | 1 | 3 |
| 4 | 2 | 1 |
| 5 | 1 | 4 |
| 6 | 1 | 5 |
| 7 | 2 | 2 |
| 8 | 3 | 1 |
| 9 | 3 | 2 |
|------|---------|---------------|
I am using InnoDB for this as it is quite heavily weighted with foreign-keys. It appears to complain when I add a second auto increment field, but I wasn't sure if there was a different way to do this?
See Question&Answers more detail:os