#! /usr/local/bin/python# basics.py - basic SQL commands tutorial# inspired from the Postgres95 tutorial # adapted to Python 1995 by Pascal ANDREprint "__________________________________________________________________"print "MODULE BASICS.PY : BASIC SQL COMMANDS TUTORIAL"printprint "This module is designed for being imported from python prompt"printprint "In order to run the samples included here, first create a connection"print "using :                        cnx = basics.DB(...)"print "then start the demo with:      basics.demo(cnx)"print "__________________________________________________________________"from pg import DBfrom pgtools import *# table creation commandsdef create_table(pgcnx):	print "-----------------------------"	print "-- Creating a table:"	print "--	a CREATE TABLE is used to create base tables. POSTGRES"	print "--	SQL has its own set of built-in types. (Note that"	print "--	keywords are case-insensitive but identifiers are "	print "--	case-sensitive.)"	print "-----------------------------"	print	print "Sending query :"	print "CREATE TABLE weather ("        print "    city            varchar(80),"        print "    temp_lo         int,"        print "    temp_hi         int,"        print "    prcp            float8,"        print "    date            date"        print ")"        pgcnx.query("CREATE TABLE weather (city varchar(80), temp_lo int," \		"temp_hi int, prcp float8, date date)")	print	print "Sending query :"	print "CREATE TABLE cities ("	print "    name		varchar(80),"	print "    location	point"	print ")"	pgcnx.query("CREATE TABLE cities ("	\		"name		varchar(80),"	\		"location	point)")# data insertion commandsdef insert_data(pgcnx):	print "-----------------------------"	print "-- Inserting data:"	print "--	an INSERT statement is used to insert a new row into"	print "--       a table. There are several ways you can specify what"	print "--	 columns the data should go to."	print "-----------------------------"	print	print "-- 1. the simplest case is when the list of value correspond to"	print "--    the order of the columns specified in CREATE TABLE."	print	print "Sending query :"	print "INSERT INTO weather "	print "   VALUES ('San Francisco', 46, 50, 0.25, '11/27/1994')"	pgcnx.query("INSERT INTO weather "	\		"VALUES ('San Francisco', 46, 50, 0.25, '11/27/1994')")	print	print "Sending query :"	print "INSERT INTO cities "	print "   VALUES ('San Francisco', '(-194.0, 53.0)')"	pgcnx.query("INSERT INTO cities "	\		"VALUES ('San Francisco', '(-194.0, 53.0)')")	print	wait_key()	print "-- 2. you can also specify what column the values correspond "	print "     to. (The columns can be specified in any order. You may "	print "     also omit any number of columns. eg. unknown precipitation"	print "     below)"	print "Sending query :"	print "INSERT INTO weather (city, temp_lo, temp_hi, prcp, date)"	print "   VALUES ('San Francisco', 43, 57, 0.0, '11/29/1994')"	pgcnx.query("INSERT INTO weather (date, city, temp_hi, temp_lo)" \		"VALUES ('11/29/1994', 'Hayward', 54, 37)")# direct selection commandsdef select_data1(pgcnx):	print "-----------------------------"	print "-- Retrieving data:"	print "--	a SELECT statement is used for retrieving data. The "	print "--	basic syntax is:"	print "--		SELECT columns FROM tables WHERE predicates"	print "-----------------------------"	print	print "-- a simple one would be the query:"	print "SELECT * FROM weather"	print 	print "The result is :"	q = pgcnx.query("SELECT * FROM weather")	print q	print	print "-- you may also specify expressions in the target list (the "	print "-- 'AS column' specifies the column name of the result. It is "	print "-- optional.)"	print "The query :"	print "   SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date "	print "   FROM weather"	print "Gives :"	print pgcnx.query("SELECT city, (temp_hi+temp_lo)/2 "	\		"AS temp_avg, date FROM weather")	print	print "-- if you want to retrieve rows that satisfy certain condition"	print "-- (ie. a restriction), specify the condition in WHERE. The "	print "-- following retrieves the weather of San Francisco on rainy "	print "-- days."	print "SELECT *"	print "FROM weather"	print "WHERE city = 'San Francisco' "	print "  and prcp > 0.0"	print pgcnx.query("SELECT * FROM weather WHERE city = 'San Francisco'" \		" AND prcp > 0.0")	print	print "-- here is a more complicated one. Duplicates are removed when "	print "-- DISTINCT is specified. ORDER BY specifies the column to sort"	print "-- on. (Just to make sure the following won't confuse you, "	print "-- DISTINCT and ORDER BY can be used separately.)"	print "SELECT DISTINCT city"	print "FROM weather"	print "ORDER BY city;"	print pgcnx.query("SELECT DISTINCT city FROM weather ORDER BY city")# selection to a temporary tabledef select_data2(pgcnx):	print "-----------------------------"	print "-- Retrieving data into other classes:"	print "--	a SELECT ... INTO statement can be used to retrieve "	print "--	data into another class."	print "-----------------------------"	print 	print "The query :"	print "SELECT * INTO TABLE temp "	print "FROM weather"	print "WHERE city = 'San Francisco' "	print "  and prcp > 0.0"	pgcnx.query("SELECT * INTO TABLE temp FROM weather " \		"WHERE city = 'San Francisco' and prcp > 0.0")	print "Fills the table temp, that can be listed with :"	print "SELECT * from temp"	print pgcnx.query("SELECT * from temp")# aggregate creation commandsdef create_aggregate(pgcnx):	print "-----------------------------"	print "-- Aggregates"	print "-----------------------------"	print	print "Let's consider the query :"	print "SELECT max(temp_lo)"	print "FROM weather;"	print pgcnx.query("SELECT max(temp_lo) FROM weather")	print 	print "-- Aggregate with GROUP BY"	print "SELECT city, max(temp_lo)"	print "FROM weather "	print "GROUP BY city;"	print pgcnx.query( "SELECT city, max(temp_lo)"	\		"FROM weather GROUP BY city")# table join commandsdef join_table(pgcnx):	print "-----------------------------"	print "-- Joining tables:"	print "--	queries can access multiple tables at once or access"	print "--	 the same table in such a way that multiple instances"	print "--	of the table are being processed at the same time."	print "-----------------------------"	print	print "-- suppose we want to find all the records that are in the "	print "-- temperature range of other records. W1 and W2 are aliases "	print "--for weather."	print	print "SELECT W1.city, W1.temp_lo, W1.temp_hi, "	print "    W2.city, W2.temp_lo, W2.temp_hi"	print "FROM weather W1, weather W2"	print "WHERE W1.temp_lo < W2.temp_lo "	print "  and W1.temp_hi > W2.temp_hi"	print	print pgcnx.query("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")	print	print "-- let's join two tables. The following joins the weather table"	print "-- and the cities table."	print	print "SELECT city, location, prcp, date"	print "FROM weather, cities"	print "WHERE name = city"	print	print pgcnx.query("SELECT city, location, prcp, date FROM weather, cities"\		" WHERE name = city")	print	print "-- since the column names are all different, we don't have to "	print "-- specify the table name. If you want to be clear, you can do "	print "-- the following. They give identical results, of course."	print	print "SELECT w.city, c.location, w.prcp, w.date"	print "FROM weather w, cities c"	print "WHERE c.name = w.city;"	print	print pgcnx.query("SELECT w.city, c.location, w.prcp, w.date " \		"FROM weather w, cities c WHERE c.name = w.city")# data updating commandsdef update_data(pgcnx):	print "-----------------------------"	print "-- Updating data:"	print "--	an UPDATE statement is used for updating data. "	print "-----------------------------"	print 	print "-- suppose you discover the temperature readings are all off by"	print "-- 2 degrees as of Nov 28, you may update the data as follow:"	print	print "UPDATE weather"	print "  SET temp_hi = temp_hi - 2,  temp_lo = temp_lo - 2"	print "  WHERE date > '11/28/1994'"	print	pgcnx.query("UPDATE weather "	\		"SET temp_hi = temp_hi - 2,  temp_lo = temp_lo - 2" \		"WHERE date > '11/28/1994'")	print	print "SELECT * from weather"	print pgcnx.query("SELECT * from weather")# data deletion commandsdef delete_data(pgcnx):	print "-----------------------------"	print "-- Deleting data:"	print "--	a DELETE statement is used for deleting rows from a "	print "--	table."	print "-----------------------------"	print	print "-- suppose you are no longer interested in the weather of "	print "-- Hayward, you can do the following to delete those rows from"	print "-- the table"	print	print "DELETE FROM weather WHERE city = 'Hayward'"	pgcnx.query("DELETE FROM weather WHERE city = 'Hayward'")	print	print "SELECT * from weather"	print	print pgcnx.query("SELECT * from weather")	print	print "-- you can also delete all the rows in a table by doing the "	print "-- following. (This is different from DROP TABLE which removes "	print "-- the table in addition to the removing the rows.)"	print	print "DELETE FROM weather"	pgcnx.query("DELETE FROM weather")	print	print "SELECT * from weather"	print pgcnx.query("SELECT * from weather")# table removal commandsdef remove_table(pgcnx):	print "-----------------------------"	print "-- Removing the tables:"	print "--	DROP TABLE is used to remove tables. After you have"	print "--	done this, you can no longer use those tables."	print "-----------------------------"	print	print "DROP TABLE weather, cities, temp"	pgcnx.query("DROP TABLE weather, cities, temp")# main demo functiondef demo(pgcnx):	create_table(pgcnx)	wait_key()	insert_data(pgcnx)	wait_key()	select_data1(pgcnx)	select_data2(pgcnx)	create_aggregate(pgcnx)	join_table(pgcnx)	update_data(pgcnx)	delete_data(pgcnx)	remove_table(pgcnx)