Ok thank you, so I can consider using clustered indexes when I need to 'reorder' random data to improve the speed of a particular query... In simple words: Clustered indexes are like the alphabetical index in a book, where term are randomly distibuted in the book and regular indexes are more like the table of content... Right? Thanks again, MaXX Jim C. Nasby wrote: > The key expense in doing an index scan is the amount of randomness > involved in reading the base table. If a table is in the same order as > the index then reading the base table will be very fast. If the table is > in a completely random order compared to an index (it's correlation is > low), then an index scan becomes very expensive because every row you > read out of the index means seeking to a random page in the table. > > So, if you do a lot of querying on the table that would work best with > an index scan, it's probably worth it to cluster on that index. > > Note that I'm talking about index *scans* here, where you're pulling a > decent number of rows. > > There's some other considerations as well, but this is probably the > biggest one. > -- MaXX ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
