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Mastering PostgreSQL 12 - Third Edition
book

Mastering PostgreSQL 12 - Third Edition

by Hans-Jürgen Schönig
November 2019
Beginner to intermediate content levelBeginner to intermediate
470 pages
11h 59m
English
Packt Publishing
Content preview from Mastering PostgreSQL 12 - Third Edition

Creating simple aggregates

For this example, the goal is to solve a very simple problem. If a customer takes a taxi, they usually have to pay for getting in the taxi—for example, 2.50. Now, let's assume that for each kilometer, the customer has to pay 2.20. The question now is, what is the total price of a trip? 

Of course, this example is simple enough to solve without a custom aggregate; however, let's see how it works. First, some test data needs to be created:

test=# CREATE TABLE t_taxi (trip_id int, km numeric);  CREATE TABLE test=# INSERT INTO t_taxi  
  VALUES (1, 4.0), (1, 3.2), (1, 4.5), (2, 1.9), (2, 4.5); INSERT 0 5 

To create aggregates, PostgreSQL offers the CREATE AGGREGATE command. The syntax of this command has become so powerful ...

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Publisher Resources

ISBN: 9781838988821Supplemental Content