Does anyone know of a thorough discussion of effective dating on the
web, particularly with respect to MySQL, or have any opinions you
could share?
I've worked with effective-dated tables in MS SQL Server and never
been particularly awe-struck by how well it works. I can think of
three ways of doing it:
1) Store a "Begin" date and an "End" date for each row and then
reference the row with 'WHERE {transaction date} BETWEEN {begin} AND
END. This inevitably winds up with overlapping rows that shouldn't
be or gaps where you don't want them, and also requires an extra date
column, but the select queries are simplest. Also, what about
indexing the dates?
2) Store an "Expires" date with each row, but then to find the actual
row you have to do a subselect or some messy joins and I'm not at all
confident this will be optimized reasonably.
3) Store an "Effective as of" date with each row but this has
essentially the same problem as 2.
None of the SQL books on my shelf even mentions this, including
Jeremy Zawodny's "Hi-Performance MySQL" and the "MySQL Reference
Manual."
This page is interesting but doesn't explain the different options
nor try to analyze which is best and under what circumstances: http://
llamasery.com/forums/showthread.php?p=34945
Strangely enough, most of what I find by googling the topic
"effective dating" has to do with meeting girls efficiently - which
is also interesting, but outside the scope of this list and not
immediately relevant to the system I'm working on.
Douglas Sims
Doug@stripped
