hmm, I'm quite curious to see what people have to say about this. My feeling is that the 2nd option would be much more efficient - as it's not really a huge amount of data - so available memory won't be an issue.

One comment though - it appears that your tables aren't very well designed. If you have the exact same set of dates in each of the five tables, then you probably should consider getting rid of that redundancy and consolidating the lot into a single table. One field for the dates, and one field for each of your five "variables".

Cheers,
Darren :)