psycopg2/examples/fetch.py

# fetch.py -- example about declaring cursors
#
# Copyright (C) 2001-2005 Federico Di Gregorio  <fog@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.
#

## put in DSN your DSN string

DSN = 'dbname=test'

## don't modify anything below tis line (except for experimenting)

import sys
import psycopg2

if len(sys.argv) > 1:
    DSN = sys.argv[1]

print "Opening connection using dns:", DSN
conn = psycopg2.connect(DSN)
print "Encoding for this connection is", conn.encoding

curs = conn.cursor()
try:
    curs.execute("CREATE TABLE test_fetch (val int4)")
except:
    conn.rollback()
    curs.execute("DROP TABLE test_fetch")
    curs.execute("CREATE TABLE test_fetch (val int4)")
conn.commit()

# we use this function to format the output

def flatten(l):
    """Flattens list of tuples l."""
    return map(lambda x: x[0], l)

# insert 20 rows in the table

for i in range(20):
    curs.execute("INSERT INTO test_fetch VALUES(%s)", (i,))
conn.commit()

# does some nice tricks with the transaction and postgres cursors
# (remember to always commit or rollback before a DECLARE)

curs.execute("DECLARE crs CURSOR FOR SELECT * FROM test_fetch")
curs.execute("FETCH 10 FROM crs")
print "First 10 rows:", flatten(curs.fetchall())
curs.execute("MOVE -5 FROM crs")
print "Moved back cursor by 5 rows (to row 5.)"
curs.execute("FETCH 10 FROM crs")
print "Another 10 rows:", flatten(curs.fetchall())
curs.execute("FETCH 10 FROM crs")
print "The remaining rows:", flatten(curs.fetchall())

# rollback to close the transaction

conn.rollback()

curs.execute("DROP TABLE test_fetch")
conn.commit()