From: "Dennis Cote"
<[EMAIL PROTECTED]>
I don't know of a way to do what you want with a user defined
function, but your example can be solved quite simply using SQL. The
following query will return a table with the required results.
select * from test order by col desc limit 3;
If you have an index on col then it will also be very fast regardless
of the size of the table, if not it will do a single table scan to
find the three maximum values.
Are you sure it will do a single scan, rather than sorting into a
temporary table and picking three topmost records? What if I want 1000
topmost records, would that still be done in a single scan? If so, how
efficiently will this temporary table of 1000 records managed?
The best algorithm for picking M largest elements out of N runs in O(N
log M), and it requires that the table of M best items seen so far be
maintained in a rather fancy data structure (a heap). Does the SQLite
query planner really implement something like that?
Igor Tandetnik
