Question

For example, I have a table of bank users (user id, user name), and a table for transactions (user id, account id, amount).
Accounts have the same properties across different users, but hold different amounts (like Alex -> Grocery, it is specific to Alex, but all other users also have Grocery account).

The question is, would it be better to create a separate table of accounts (account id, user id, amount left) or to get this value by selecting all transactions with the needed user id and account id and just summing the ‘amount’ values? It seems that the first approach would be faster, but more prone to error and database corruption – I would need to update accounts every time the transaction happens. The second approach seems to be cleaner, but would it lead to significant speed reduction?

What would you recommend?

Answer 1

good question!

In my opinion you should always avoid duplicated data so I would go with the “summing” every time option

“It seems that the first approach would be faster, but more prone to error and database corruption – I would need to update accounts every time the transaction happens”

said everything, you are subject to errors and you’ll have to build a mechanism to maintain the data up-to-date.

Dont forget that the first approach would be faster to select only. inserts updates and deletes would be slower because you will have to update your second table.