basics.source

---------------------------------------------------------------------------
--
-- basics.sql-
--    Tutorial on the basics (table creation and data manipulation)
--
--
-- Copyright (c) 1994, Andrew Yu, University of California
--
-- $Id: basics.source,v 1.3 1999/07/08 15:27:01 momjian Exp $
--
---------------------------------------------------------------------------

-----------------------------
-- Creating a table:
--	a CREATE TABLE is used to create base tables. POSTGRES SQL has
--	its own set of built-in types. (Note that keywords are case-
--	insensitive but identifiers are case-sensitive.)
-----------------------------

CREATE TABLE weather (
	city		varchar(80),
	temp_lo		int,		-- low temperature
	temp_hi		int,		-- high temperature
	prcp		float8,		-- precipitation
	date		date
);

CREATE TABLE cities (
	name		varchar(80),
	location	point
);

-----------------------------
-- Inserting data:
--	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, '11/27/1994');

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.
--    eg. unknown precipitation below)

INSERT INTO weather (city, temp_lo, temp_hi, prcp, date)
   VALUES ('San Francisco', 43, 57, 0.0, '11/29/1994');

INSERT INTO weather (date, city, temp_hi, temp_lo)
   VALUES ('11/29/1994', 'Hayward', 54, 37);


-----------------------------
-- Retrieving data:
--	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 (ie. 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;

-----------------------------
-- Retrieving data into other classes:
--	a SELECT ... INTO statement can be used to retrieve data into
--	another class.
-----------------------------

SELECT * INTO TABLE mytemp 
FROM weather
WHERE city = 'San Francisco' 
   and prcp > 0.0;

SELECT * from mytemp;

-----------------------------
-- Aggregates
-----------------------------

SELECT max(temp_lo)
FROM weather;

-- Aggregate with GROUP BY
SELECT city, max(temp_lo)
FROM weather 
GROUP BY city;

-----------------------------
-- Joining 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.
-----------------------------

-- 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, weather W2
WHERE W1.temp_lo < W2.temp_lo 
   and W1.temp_hi > W2.temp_hi;

-- let's join two tables. The following joins the weather table
-- and the cities table.

SELECT city, location, prcp, date
FROM weather, cities
WHERE name = city;

-- 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 w.city, c.location, w.prcp, w.date
FROM weather w, cities c
WHERE c.name = w.city;

-----------------------------
-- Updating data:
--	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 > '11/28/1994';

SELECT * from weather;


-----------------------------
-- Deleting data:
--	a DELETE statement is used for deleting rows from a table.
-----------------------------

-- suppose you are no longer interested in the weather of Hayward, 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, mytemp;