Comparative Window Functions: Proposed Extensions to Analytic Functions
I promise that this will be the last post on analytic functions this month; but I came across this proposal to extend analytic functions with a comparative window function on Tom Kyte’s blog yesterday (also make sure to review the actual paper). Basically this new type of analytic function would allow you to compare the current row in a window to any other row in the window. I recently had a requirement where this would have come in handy. Imagine a dataset made up of product category, product id, product referential id, e.g.:
Computers,1,2
Computers,1,3
Computers,1,4
Computers,4,9
The requirement was to find those products whose reference products were also in the dataset. In the example above this would have been the record Computers,1,4. Something that can only be easily solved with a self-join. With this new proposal you could write this as
|
1 2 3 4 5 6 7 8 9 10 |
SELECT * FROM ( SELECT prod_cat. prod_id. prod_ref_id, MAX(CASE WHEN prod_ref_id = INDEX(prod_id,anchor_row) THEN 1 ELSE 0) OVER (PARTITION BY prod_cat ROWS BETWEEN UNBOUNDED PRECEDING UNBOUNDED FOLLOWING) ref_exists_ind FROM prod_ref ) WHERE ref_exists_ind = 1 |
Pretty cool…
