db-derby-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Rick Hillegas <rick.hille...@oracle.com>
Subject Re: trigger with cascade delete problem
Date Fri, 13 Jun 2014 12:59:49 GMT
Hi Tim,

I still don't think I understand what's not working. Here's my crude 

1) You have 3 tables:

MAIN - This contains the information to be aggregated.

GROUPING - This contains facts needed to group the information in MAIN

AGGREGATES - This contains a pre-computed, grouped aggregation of MAIN, 
using the groups in GROUPING

2) A foreign key from MAIN to GROUPING defines the groups. It's unclear 
whether a similar foreign key links AGGREGATES to GROUPING.

3) When you delete a group from GROUPING, cascade actions delete the 
rows in the group from MAIN. And some triggers bring AGGREGATES back 
into agreement with the facts in MAIN and GROUPING.

I understand why deleting a group means that you need to delete the 
corresponding aggregated result for that group from AGGREGATES. What I 
don't understand is why you need to do anything else to AGGREGATES. Is 
what's in AGGREGATES not simply the result of a grouped aggregation?

I don't think I can speculate further without knowing more about how the 
contents of AGGREGATES are calculated. I understand that this may be the 
special sauce of your application which you don't want to share. Maybe 
you can share a simplified problem which shows why this aggregation is 
so tricky.


View raw message