Aggregated variable only work with transaction in Query Browser?

[Cat T]

I want to select rows and use user variable to generate an incremental id for the result. For example, I want the following query

select @id:=(@id+1) as id from file_list limit 5

to return 5 rows with values 1 to 5. However, the result is

+------+
| id |
+------+
| NULL |
| NULL |
| NULL |
| NULL |
| NULL |
+------+
5 rows in set (0.00 sec)

I got the same result in MySQL Query Browser too. If I click on the "Start Transaction" button in MySql Query Browser then excute the query, then the result looks OK with 5 values from 1 to 5. However, if I excute the same query again, it will return 6 to 10.

Can somebody give me some explainations on this? Thanks a lot.

T Cat