Want to add a "variable" to a table

Question

I'm using PostgreSQL 8.4 and I have a table that is cleared out and refilled with new data every so often. I want to be able to store the date that the table was last filled, but I'm not sure where to put it. I'm really a novice at database design, and the only two things I can think of are:

1. Create a table with the sole purpose of storing the date
2. Timestamp every row in the table with the same timestamp

There's about 1000 to 2000 rows normally. It's just for a hobby project. Any help will be greatly appreciated.

Answer 1

Timestamping each row doesn't seem to make a lot of sense to me. I would just keep a log of the events that are interesting. Such a log could be reusable for other events too. E.g. (sorry this is SQL Server dialect, you may have to adjust slightly):

CREATE TABLE dbo.EventLog
(
  EventDate SMALLDATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  [Description] NVARCHAR(2000)
);

Whenever you reload the table, also call a stored procedure that does this:

INSERT dbo.EventLog([Description])
  SELECT N'Re-populated table x';

If you need to know the date of the last refresh, you can say:

SELECT MAX(EventDate) FROM dbo.EventLog
  WHERE [Description] = N'Re-populated table x';

If all you ever care about is the last time, then before the insert above, you could just:

DELETE dbo.EventLog
  WHERE [Description] = N'Re-populated table x';