James Harper wrote: > The subquery returns a very small result set (0 or 1, assuming you use > DISTINCT) and so isn't too inefficient. It's when you say 'WHERE NOT > EXISTS (SOME QUERY WITH LOTS OF RESULTS)' that you start to really bog > down
True, but if the outer query contains a very large number of records, the inner query is executed over and over and over and ... This multiplies the small execution time by a large number. Think of it like a WHILE loop that executes a block of code each time round. The inner block of code might be quick, but if the loop goes round several million times, the cumulative time becomes significant. One general rule of thumb of SQL execution is that bulk processing is almost always faster than processing records individually in a loop. -- Mike Holden ------------------------------------------------------------------------------ Crystal Reports - New Free Runtime and 30 Day Trial Check out the new simplified licensing option that enables unlimited royalty-free distribution of the report engine for externally facing server and web deployment. http://p.sf.net/sfu/businessobjects _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
