Mark Walker wrote:
> I'm not sure what you're trying to do but, it appears that you database
> design is incorrect. What you need is something like
>
> CREATE TABLE temp_readings
> (
> _date Date,
> temperature double,
> source varchar(20),
> )
>
> No reading, no record. Are you suggesting that you would have a weekly
> set of records for each row?
>
> CREATE TABLE temp_readings
> (
> weekstart date,
> sun double,
> mon double,
> tues, double
> etc
> )
>
> Not such a great way to do it.
Ummm, I'm not trying to make a temperature database. I was responding to
the previous poster with an extremely simple example of usefulness of
the _concept_ of "null". I'm afraid I hadn't considered the possibility
that it would be mistaken as an example of an actual table.
But since you bring it up, simply omitting rows isn't necessarily an
option. A common scenario for weather observation is to take regular
snapshots or a bunch of measurements (air-temperature, humidity,
wind-speed, soil-temperature, leaf-wetness, UV radiation, etc.) which
can easily be represented in a table with a timestamp and a column for
each of the measurements. In a modular weather station where a specific
instrument can be out of service, one or more of those measurements
could be missing (null) for a period of time while the remaining
measurements are still being inserted.
Cheers,
Steve
