On Fri, Jul 17, 2015 at 11:32 AM, Ken Dibble <krdib...@stny.rr.com> wrote: > > My previous understanding was that if there is a WHERE clause or an ORDER BY > clause in the query, then VFP always creates the temp file on disk. >
My belief is very similar to yours, but a little different. If the SQL engine can give you the result you request by the equivalent of a SET FILTER on the underlying table OR with a temporary IDX (for the order clause), it will do this, essentially, taking your: select * from mytable where somefield = somevalue order by someotherfield what I imagine that FoxPro does is: use mytable again in 0 noupdate alias Query select Query set fields to <fieldlist> to filter the columns displayed, if you don't specify "*" in your select statement set filter on somefield = somevalue index on someotherfield to mytempidxname -- gives you exactly the same effect with no need to write records to disk or copy them to a temp cursor, speeding the result. Now, in many, many cases, this query result is perfectly acceptable for what you need it to do. The only issues come up if you ASSuME :) you can do things with a query result that you shouldn't do.. If you want to be CERTAIN that you are getting a new data file on disk/in memory disconnected from the original source, you can: (1) change the structure by adding a field not in the original source, even a .t. as dummyfield, to the field list. (2) use READWRITE or NOFILTER, depending on your needs (3) specify an INTO TABLE result. Whew. A lot of nit-picky discussion on a fine point. As part of the Rushmore and SQL parsing engine processing, speed is a high priority. Where something can be done in memory in nanoseconds, that's preferred to network access in microseconds, and that's preferred to disk drive access in milliseconds. -- Ted Roche Ted Roche & Associates, LLC http://www.tedroche.com _______________________________________________ Post Messages to: ProFox@leafe.com Subscription Maintenance: http://mail.leafe.com/mailman/listinfo/profox OT-free version of this list: http://mail.leafe.com/mailman/listinfo/profoxtech Searchable Archive: http://leafe.com/archives/search/profox This message: http://leafe.com/archives/byMID/profox/cacw6n4swtcl3psqid2iq76nxyt9k-fkhv+8twlvrogadk3a...@mail.gmail.com ** All postings, unless explicitly stated otherwise, are the opinions of the author, and do not constitute legal or medical advice. This statement is added to the messages for those lawyers who are too stupid to see the obvious.
