keep counter vs count on fly

[chill2k66]

I have a database of users who can have any number of friends. Sometimes, I just need the total number of friends (without need for whom they are). From a practical and efficiency standpoint, would it be wise to have a running counter of friends as a column for each user? This is in contrast to running a query each time on a friends' database to count the number of rows returned. Is there any standard for this?

[earl-grey]

If the query is run very often, it's fine to denormalize. But, for better guaranteed consistency, you can put the counter updates in insert/delete triggers on friends relationship table, rather than in your server-side code.

[chill2k66]

Yeah, I just thought it wouldn't be efficient to pull out 5 rows each time from a 1 million row database 10 times each page.