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For the purposes of this discussion, row_number() is just as good as rank(), and its behavior is easier to understand and describe. So let's switch the examples to using row_number(). Along the way to checking the results given in the tutorial, I found it helpful to extract the empsalary table we use in the regression tests, which is evidently the same data that was used to make these results. So I shoved that into advanced.source to improve the coverage of that file a little. (There's still several pages of the tutorial that are not included in it, but at least now 3.5 Window Functions is covered.) Suggested-by: "David G. Johnston" <david.g.johnston@gmail.com> Author: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://postgr.es/m/173737973383.1070.1832752929070067441@wrigleys.postgresql.org
110 lines
2.8 KiB
Plaintext
110 lines
2.8 KiB
Plaintext
---------------------------------------------------------------------------
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--
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-- advanced.sql-
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-- Tutorial on advanced PostgreSQL features
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--
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--
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-- Copyright (c) 1994, Regents of the University of California
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--
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-- src/tutorial/advanced.source
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--
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---------------------------------------------------------------------------
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-----------------------------
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-- Window Functions
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-----------------------------
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-- a sample table
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CREATE TABLE empsalary (
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depname text,
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empno bigint,
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salary int,
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enroll_date date
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);
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INSERT INTO empsalary VALUES
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('develop', 10, 5200, '2007-08-01'),
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('sales', 1, 5000, '2006-10-01'),
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('personnel', 5, 3500, '2007-12-10'),
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('sales', 4, 4800, '2007-08-08'),
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('personnel', 2, 3900, '2006-12-23'),
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('develop', 7, 4200, '2008-01-01'),
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('develop', 9, 4500, '2008-01-01'),
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('sales', 3, 4800, '2007-08-01'),
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('develop', 8, 6000, '2006-10-01'),
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('develop', 11, 5200, '2007-08-15');
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SELECT depname, empno, salary, avg(salary) OVER (PARTITION BY depname)
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FROM empsalary;
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SELECT depname, empno, salary,
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row_number() OVER (PARTITION BY depname ORDER BY salary DESC)
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FROM empsalary;
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SELECT salary, sum(salary) OVER () FROM empsalary;
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SELECT salary, sum(salary) OVER (ORDER BY salary) FROM empsalary;
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SELECT depname, empno, salary, enroll_date
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FROM
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(SELECT depname, empno, salary, enroll_date,
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row_number() OVER (PARTITION BY depname ORDER BY salary DESC, empno) AS pos
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FROM empsalary
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) AS ss
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WHERE pos < 3;
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SELECT sum(salary) OVER w, avg(salary) OVER w
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FROM empsalary
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WINDOW w AS (PARTITION BY depname ORDER BY salary DESC);
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DROP TABLE empsalary;
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-----------------------------
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-- Inheritance:
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-- A table can inherit from zero or more tables. A query can reference
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-- either all rows of a table or all rows of a table plus all of its
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-- descendants.
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-----------------------------
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-- For example, the capitals table inherits from cities table. (It inherits
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-- all data fields from cities.)
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CREATE TABLE cities (
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name text,
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population float8,
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elevation int -- (in ft)
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);
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CREATE TABLE capitals (
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state char(2)
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) INHERITS (cities);
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-- Now, let's populate the tables.
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INSERT INTO cities VALUES ('San Francisco', 7.24E+5, 63);
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INSERT INTO cities VALUES ('Las Vegas', 2.583E+5, 2174);
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INSERT INTO cities VALUES ('Mariposa', 1200, 1953);
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INSERT INTO capitals VALUES ('Sacramento', 3.694E+5, 30, 'CA');
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INSERT INTO capitals VALUES ('Madison', 1.913E+5, 845, 'WI');
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SELECT * FROM cities;
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SELECT * FROM capitals;
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-- You can find all cities, including capitals, that
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-- are located at an elevation of 500 ft or higher by:
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SELECT c.name, c.elevation
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FROM cities c
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WHERE c.elevation > 500;
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-- To scan rows of the parent table only, use ONLY:
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SELECT name, elevation
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FROM ONLY cities
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WHERE elevation > 500;
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-- clean up (you must remove the children first)
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DROP TABLE capitals;
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DROP TABLE cities;
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