A warm welcome to our newest attendee’s from Indiana! Glad the weather was nice enough to come to the meeting and discover what we are all about.
Advisor VFP DevCon 2007 has been announced to be held on May 6-10, 2007 in Anaheim, California.
Andy Kramek gave a really great talk on advanced SQL Queries and Intellisense.
A small example of things I learned in this session:
Unless you ‘force’ the query SQL might do the query join’s in a different order then you have specified. It will join tables which will narrow the query down to the fewest records. Force, however, will slow the query down dramatically. The force also only relates to the join, not to the filter. This is why you don’t use ‘force’ all the time. Because you really might have wanted it to do the “and” filter condition first.
Union is really doing a scatter gather, not an append.
Union is really “union distinct”. Append results sets and remove duplicate records. Union all has both either way.
An Existence subquery stops when it reaches the first matching query. When it finds one record that meets the first condition. If you say select where equals it will look for all of them.
Uncorrelated subqueries handle queries involving unrelated siblings and avoids having to hard code values. Unrelated siblings are tables that both individually relate to the same parent record but do not directly relate to each other.
Correlated subquery is going to run for every record in the main table, but it is extremely fast if you can keep it simple. But if you can get away with a join, do that instead. But it is more efficient then unions or repeated queries. (running the query in a loop for different years)
This was just a taste of all Andy discussed at the meeting. GRAFUG members will be able to download Andy’s white papers from the GRAFUG website available soon.
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