Sum up values in SQL once all values are available
- by James Brown
I have events flowing into a MySQL database and I need to group and sum the events to transactions and store away into another table. The data looks like:
+----+---------+------+-------+
| id | transid | code | value |
+----+---------+------+-------+
| 1 | 1 | b | 12 |
| 2 | 1 | i | 23 |
| 3 | 2 | b | 34 |
| 4 | 1 | e | 45 |
| 5 | 3 | b | 56 |
| 6 | 2 | i | 67 |
| 7 | 2 | e | 78 |
| 8 | 3 | i | 89 |
| 9 | 3 | i | 90 |
+----+---------+------+-------+
The events arrive in batches and I would like to create the transaction by summing up the values for each transid, like:
select transid, sum(value) from eventtable group by transid;
but only after all the events for that transid have arrived. That is determined by the event with the code e (b for the beginning, e for the end and i for varying amount of intermediates). Being a novice in SQL, how could I implement the requirement for the existance of the end code before the summing?
