> -----Original Message----- > From: pgsql-bugs-ow...@postgresql.org [mailto:pgsql-bugs- > ow...@postgresql.org] On Behalf Of w...@devauld.ca > Sent: Tuesday, November 20, 2012 10:28 AM > To: pgsql-bugs@postgresql.org > Subject: [BUGS] BUG #7685: last_value() not consistent throughout window > partition > > The following bug has been logged on the website: > > Bug reference: 7685 > Logged by: Wes Devauld > Email address: w...@devauld.ca > PostgreSQL version: 9.2.1 > Operating system: Windows 7 Enterprise > Description: > > -- The last_value(0 window function appears to be changing values > -- mid window. An example is detailed below. > > ----SELECT version(); > -- version > ------------------------------------------------------------- > -- PostgreSQL 9.1.6, compiled by Visual C++ build 1500, 32-bit > > ------------------------- > > -- **** DB DUMP **** > -- > -- PostgreSQL database dump > -- > > -- Dumped from database version 9.1.4 > -- Dumped by pg_dump version 9.1.4 > -- Started on 2012-11-19 15:01:41 > > SET statement_timeout = 0; > SET client_encoding = 'UTF8'; > SET standard_conforming_strings = on; > SET check_function_bodies = false; > SET client_min_messages = warning; > > SET search_path = public, pg_catalog; > > SET default_tablespace = ''; > > SET default_with_oids = false; > > -- > -- TOC entry 170 (class 1259 OID 25186) > -- Dependencies: 5 > -- Name: bug_report; Type: TABLE; Schema: public; Owner: postgres; > Tablespace: > -- > > CREATE TABLE bug_report ( > d1 date NOT NULL, > d2 date NOT NULL, > v real NOT NULL > ); > > > ALTER TABLE public.bug_report OWNER TO postgres; > > -- > -- TOC entry 1880 (class 0 OID 25186) > -- Dependencies: 170 > -- Data for Name: bug_report; Type: TABLE DATA; Schema: public; Owner: > postgres > -- > > COPY bug_report (d1, d2, v) FROM stdin; > 2012-11-19 2012-11-07 358363 > 2012-11-18 2012-11-07 358363 > 2012-11-17 2012-11-07 358363 > 2012-11-16 2012-11-07 257572 > 2012-11-15 2012-11-07 257572 > 2012-11-14 2012-11-07 257572 > 2012-11-13 2012-11-07 257572 > 2012-11-12 2012-11-07 257572 > 2012-11-11 2012-11-07 257572 > 2012-11-10 2012-11-07 257572 > \. > > > -- Completed on 2012-11-19 15:01:42 > > --**** Description **** > > select d2, last_value(v) over (partition by d2 order by d1), > first_value(v) over (partition by d2 order by d1 desc) from > bug_report > > --Returns: > --"2012-11-07";358363;358363 > --"2012-11-07";358363;358363 > --"2012-11-07";358363;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > --"2012-11-07";257572;358363 > > --You can see that the last_value() > --switches in the middle of the > --partition for the window function > --when both columns should be > --identical since the first/last > --and asc/desc changes should > --cancel each other out. > > > --Thanks, and good work with the product. >
Not A Bug. When you add an "Order By" the resultant window FRAME is from the first record (of the partition) up-to-and-including the current record (of the partition); no "future" records (in the partition) are part of the window FRAME. Thus for "last_value" you are always implicitly referring to the current row (of the FRAME). This is defined and documented behavior. In order to use "last_value" you need to override the FRAME that the window operates on to include all rows. http://www.postgresql.org/docs/9.2/interactive/functions-window.html - read the second paragraph following the table and explore from there David J. -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
