Index scans and index-only scans

An example of an index scan is the earlier query. As there is an index on the user column and we asked for all the user details, after the value is found in the index, Postgre then goes to the heap and fetches the other fields.

An index-only scan means that all the needed information is found in the index and there is no need to go to memory. This is useful when querying a pair of fields multiple times - creating an index on those fields will output quicker results.