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# 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()
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