What type of index should be used for querying account_id and created_at?

For a query that filters or sorts data by the fields account_id and created_at, the optimal approach is to use a composite (multi-column) index that includes both fields. For example, in SQL, you can create an index like:

CREATE INDEX idx_account_created ON table_name (account_id, created_at);

This index will efficiently support queries where filtering or sorting is first done by account_id, then by created_at. If queries frequently use both fields together, this will significantly speed up the retrieval. If queries are only on one of the fields, consider creating separate indexes for each.

It is important to consider the order of fields in the index: the field most frequently used for filtering or grouping should come first.