SQL & PL/SQL

I'm not sure if this forum is the correct place to post this question.

Our data has missing values because we only add records when the data changes. For example, we read integer values from a meter every 15 minutes, but if the value changed only once in the last hour, only one value is recorded instead of four. The problem occurs when we want to run a calculation that expects four values, not just one. In this case, we do not have to generate the missing using statistical means because we know what the missing values are.

I have to assume this is a common problem. Rather than inserting the missing values into the database, I would rather generate them on the fly when the database is queried. Are there commonly accepted techniques for handling this? Can anyone point me to some information resources?

Thanks in advance