On Fri, Jul 11, 2014 at 1:13 PM, Gene Wirchenko <[email protected]> wrote:
> At 02:58 2014-07-11, Dave Crozier <[email protected]> wrote: > >> Readwrite has the same effect as NoFilter and also allows you to write to >> the cursor. >> > > The docs do not support your statement. There is nothing under SQL > SELECT stating that READWRITE would necessarily use or not use a temporary > cursor. To be safe, I have the odd filter created using both options. > > What are these "docs" of which you speak? I checked the (extremely rare) PDF version of HackFox 7b and Tamar says, "Before VFP 7, cursors created by SELECT-SQL were always read-only. You couldn't change the data in them either interactively or programmatically. In VFP 7, the new READWRITE clause indicates that the cursor created should be (surprise) read-write. In FoxPro 2.x, read-only cursors were an important, frustrating limitation. In Visual FoxPro, it didn't matter too much. If you needed to be able to update cursor contents, you could use a view instead of a query to create the cursor. There's actually a way around this limit, even in FoxPro 2.x. As long as the query creates a "real" cursor and not just a filter of the original table, you can USE the cursor AGAIN in another work area and it's read-write there.) VFP 5 added the NOFILTER clause for INTO CURSOR. In order to do things as fast as it can, FoxPro pulls a little trick. If a query involves only a single table, has no calculated fields, is fully optimizable, and is sent to a cursor, rather than going to the trouble of creating a whole new cursor, FoxPro simply filters the original table. Often, that's good enough for whatever you have in mind. However, in some situations, especially those where the query result is then used in a subsequent query or where you want to index the cursor, having only a filtered view of the original causes problems. In VFP 3 and earlier versions, you worked around this by putting something in the query that outwitted FoxPro. Starting in VFP 5, it's a lot easier—just add NOFILTER to the query and FoxPro always creates a real cursor. (Doesn't "real cursor" sound like an oxymoron?) Although you can include both READWRITE and NOFILTER in a query, NOFILTER is unnecessary. By definition, any read-write cursor is not just a filter of the original table. " -- Ted Roche Ted Roche & Associates, LLC http://www.tedroche.com --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html --- _______________________________________________ Post Messages to: [email protected] 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/CACW6n4scSsSD3quZiZHAVDCZ5TS+qYCREboX3BY24SX=fve...@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.
