Vertica Quick Tip: The LIMIT Analytic Function

SarahLSarahL Administrator, Moderator, Employee, Registered User, VerticaExpert, CABuser, VerticaPartners
edited January 2018 in Vertica Tips

This tip was authored by Jim Knicely.

Vertica contains an abundance of built-in SQL analytic functions. One of the lesser known but also one of the coolest is the LIMIT analytic function.

Example
Say I have the following table data:

=> SELECT * FROM limit_test;
  the_date  | test_num | test_desc
------------+----------+-----------
2018-01-10 |        1 | TEST1
2018-01-10 |        2 | TEST2
2018-01-12 |        1 | TEST
2018-01-11 |        2 | TEST2
2018-01-11 |        3 | TEST3
(5 rows)

But I only want to see the latest test number for each date. For that I can use the LIMIT analytic function!

=> SELECT * 
->   FROM (SELECT the_date, test_num, test_desc
(>           FROM limit_test
(>          LIMIT 1 OVER (PARTITION BY the_date order by test_num DESC)) foo
->  ORDER BY the_date;
  the_date  | test_num | test_desc
------------+----------+-----------
2018-01-10 |        2 | TEST2
2018-01-11 |        3 | TEST3
2018-01-12 |        1 | TEST
(3 rows)
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