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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:15:05 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:15:05 +0000
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Adding upstream version 14.5.upstream/14.5upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+---------------------------------------------------------------------------
+--
+-- basics.sql-
+-- Tutorial on the basics (table creation and data manipulation)
+--
+--
+-- src/tutorial/basics.source
+--
+---------------------------------------------------------------------------
+
+-----------------------------
+-- Creating a New Table:
+-- A CREATE TABLE is used to create base tables. PostgreSQL has
+-- its own set of built-in types. (Note that SQL is case-
+-- insensitive.)
+-----------------------------
+
+CREATE TABLE weather (
+ city varchar(80),
+ temp_lo int, -- low temperature
+ temp_hi int, -- high temperature
+ prcp real, -- precipitation
+ date date
+);
+
+CREATE TABLE cities (
+ name varchar(80),
+ location point
+);
+
+
+-----------------------------
+-- Populating a Table With Rows:
+-- An INSERT statement is used to insert a new row into a table. There
+-- are several ways you can specify what columns the data should go to.
+-----------------------------
+
+-- 1. The simplest case is when the list of value correspond to the order of
+-- the columns specified in CREATE TABLE.
+
+INSERT INTO weather
+ VALUES ('San Francisco', 46, 50, 0.25, '1994-11-27');
+
+INSERT INTO cities
+ VALUES ('San Francisco', '(-194.0, 53.0)');
+
+-- 2. You can also specify what column the values correspond to. (The columns
+-- can be specified in any order. You may also omit any number of columns,
+-- e.g., unknown precipitation below.
+
+INSERT INTO weather (city, temp_lo, temp_hi, prcp, date)
+ VALUES ('San Francisco', 43, 57, 0.0, '1994-11-29');
+
+INSERT INTO weather (date, city, temp_hi, temp_lo)
+ VALUES ('1994-11-29', 'Hayward', 54, 37);
+
+
+-----------------------------
+-- Querying a Table:
+-- A SELECT statement is used for retrieving data. The basic syntax is
+-- SELECT columns FROM tables WHERE predicates.
+-----------------------------
+
+-- A simple one would be:
+
+SELECT * FROM weather;
+
+-- You may also specify expressions in the target list. (The 'AS column'
+-- specifies the column name of the result. It is optional.)
+
+SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather;
+
+-- If you want to retrieve rows that satisfy certain condition (i.e., a
+-- restriction), specify the condition in WHERE. The following retrieves
+-- the weather of San Francisco on rainy days.
+
+SELECT *
+ FROM weather
+ WHERE city = 'San Francisco'
+ AND prcp > 0.0;
+
+-- Here is a more complicated one. Duplicates are removed when DISTINCT is
+-- specified. ORDER BY specifies the column to sort on. (Just to make sure the
+-- following won't confuse you, DISTINCT and ORDER BY can be used separately.)
+
+SELECT DISTINCT city
+ FROM weather
+ ORDER BY city;
+
+
+-----------------------------
+-- Joins Between Tables:
+-- queries can access multiple tables at once or access the same table
+-- in such a way that multiple instances of the table are being processed
+-- at the same time.
+-----------------------------
+
+-- The following joins the weather table and the cities table.
+
+SELECT * FROM weather JOIN cities ON city = name;
+
+-- This prevents a duplicate city name column:
+
+SELECT city, temp_lo, temp_hi, prcp, date, location
+ FROM weather JOIN cities ON city = name;
+
+-- since the column names are all different, we don't have to specify the
+-- table name. If you want to be clear, you can do the following. They give
+-- identical results, of course.
+
+SELECT weather.city, weather.temp_lo, weather.temp_hi, weather.prcp, weather.date, cities.location
+ FROM weather JOIN cities ON weather.city = cities.name;
+
+-- Old join syntax
+
+SELECT *
+ FROM weather, cities
+ WHERE city = name;
+
+-- Outer join
+
+SELECT *
+ FROM weather LEFT OUTER JOIN cities ON weather.city = cities.name;
+
+-- Suppose we want to find all the records that are in the temperature range
+-- of other records. w1 and w2 are aliases for weather.
+
+SELECT w1.city, w1.temp_lo, w1.temp_hi,
+ w2.city, w2.temp_lo, w2.temp_hi
+FROM weather w1 JOIN weather w2
+ ON w1.temp_lo < w2.temp_lo AND w1.temp_hi > w2.temp_hi;
+
+
+-----------------------------
+-- Aggregate Functions
+-----------------------------
+
+SELECT max(temp_lo)
+ FROM weather;
+
+SELECT city FROM weather
+ WHERE temp_lo = (SELECT max(temp_lo) FROM weather);
+
+-- Aggregate with GROUP BY
+SELECT city, max(temp_lo)
+ FROM weather
+ GROUP BY city;
+
+-- ... and HAVING
+SELECT city, max(temp_lo)
+ FROM weather
+ GROUP BY city
+ HAVING max(temp_lo) < 40;
+
+
+-----------------------------
+-- Updates:
+-- An UPDATE statement is used for updating data.
+-----------------------------
+
+-- Suppose you discover the temperature readings are all off by 2 degrees as
+-- of Nov 28, you may update the data as follow:
+
+UPDATE weather
+ SET temp_hi = temp_hi - 2, temp_lo = temp_lo - 2
+ WHERE date > '1994-11-28';
+
+SELECT * FROM weather;
+
+
+-----------------------------
+-- Deletions:
+-- A DELETE statement is used for deleting rows from a table.
+-----------------------------
+
+-- Suppose you are no longer interested in the weather of Hayward, then you can
+-- do the following to delete those rows from the table.
+
+DELETE FROM weather WHERE city = 'Hayward';
+
+SELECT * FROM weather;
+
+-- You can also delete all the rows in a table by doing the following. (This
+-- is different from DROP TABLE which removes the table in addition to the
+-- removing the rows.)
+
+DELETE FROM weather;
+
+SELECT * FROM weather;
+
+
+-----------------------------
+-- Removing the tables:
+-- DROP TABLE is used to remove tables. After you have done this, you
+-- can no longer use those tables.
+-----------------------------
+
+DROP TABLE weather, cities;