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ibm_db-free_result.py
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ibm_db-free_result.py
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#! /usr/bin/python3
#-------------------------------------------------------------------------------------------------#
# NAME: ibm_db-free_result.py #
# #
# PURPOSE: This program is designed to illustrate how to use the ibm_db.free_result() API to #
# free system resources associated with a prepared SQL statement. #
# #
# Additional APIs used: #
# ibm_db.prepare() #
# ibm_db.execute() #
# ibm_db.num_rows() #
# ibm_db.set_option() #
# #
# USAGE: Log in as a Db2 database instance user (for example, db2inst1) and issue the #
# following command from a terminal window: #
# #
# ./ibm_db-free_result.py #
# #
#-------------------------------------------------------------------------------------------------#
# DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITY #
# #
# (C) COPYRIGHT International Business Machines Corp. 2018, 2019 All Rights Reserved #
# Licensed Materials - Property of IBM #
# #
# US Government Users Restricted Rights - Use, duplication or disclosure restricted by GSA ADP #
# Schedule Contract with IBM Corp. #
# #
# The following source code ("Sample") is owned by International Business Machines Corporation #
# or one of its subsidiaries ("IBM") and is copyrighted and licensed, not sold. You may use, #
# copy, modify, and distribute the Sample in any form without payment to IBM, for the purpose #
# of assisting you in the creation of Python applications using the ibm_db library. #
# #
# The Sample code is provided to you on an "AS IS" basis, without warranty of any kind. IBM #
# HEREBY EXPRESSLY DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT #
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. #
# Some jurisdictions do not allow for the exclusion or limitation of implied warranties, so the #
# above limitations or exclusions may not apply to you. IBM shall not be liable for any damages #
# you suffer as a result of using, copying, modifying or distributing the Sample, even if IBM #
# has been advised of the possibility of such damages. #
#-------------------------------------------------------------------------------------------------#
# Load The Appropriate Python Modules
import sys # Provides Information About Python Interpreter Constants, Functions, & Methods
import ibm_db # Contains The APIs Needed To Work With Db2 Databases
#-------------------------------------------------------------------------------------------------#
# Import The Db2ConnectionMgr Class Definition, Attributes, And Methods That Have Been Defined #
# In The File Named "ibm_db_tools.py"; This Class Contains The Programming Logic Needed To #
# Establish And Terminate A Connection To A Db2 Server Or Database #
#-------------------------------------------------------------------------------------------------#
from ibm_db_tools import Db2ConnectionMgr
#-------------------------------------------------------------------------------------------------#
# Import The ipynb_exit Class Definition, Attributes, And Methods That Have Been Defined In The #
# File Named "ipynb_exit.py"; This Class Contains The Programming Logic Needed To Allow "exit()" #
# Functionality To Work Without Raising An Error Or Stopping The Kernel If The Application Is #
# Invoked In A Jupyter Notebook #
#-------------------------------------------------------------------------------------------------#
from ipynb_exit import exit
# Define And Initialize The Appropriate Variables
dbName = "SAMPLE"
userID = "db2inst1"
passWord = "Passw0rd"
dbConnection = None
preparedStmt = False
resultSet = False
returnCode = False
# Create An Instance Of The Db2ConnectionMgr Class And Use It To Connect To A Db2 Database
conn = Db2ConnectionMgr('DB', dbName, '', '', userID, passWord)
conn.openConnection()
if conn.returnCode is True:
dbConnection = conn.connectionID
else:
conn.closeConnection()
exit(-1)
# Define The SQL Statement That Is To Be Executed
sqlStatement = "SELECT * FROM employee WHERE edlevel > 17"
# Prepare The SQL Statement Just Defined
print("Preparing the SQL statement \"" + sqlStatement + "\" ... ", end="")
try:
preparedStmt = ibm_db.prepare(dbConnection, sqlStatement)
except Exception:
pass
# If The SQL Statement Could Not Be Prepared By Db2, Display An Error Message And Exit
if preparedStmt is False:
print("\nERROR: Unable to prepare the SQL statement specified.")
conn.closeConnection()
exit(-1)
# Otherwise, Complete The Status Message
else:
print("Done!\n")
# Execute The SQL Statement Just Prepared
print("Executing the prepared SQL statement ... ", end="")
try:
resultSet = ibm_db.execute(preparedStmt)
except Exception:
pass
# If The SQL Statement Could Not Be Executed, Display An Error Message And Exit
if resultSet is False:
print("\nERROR: Unable to execute the SQL statement specified.")
conn.closeConnection()
exit(-1)
# Otherwise, Complete The Status Message
else:
print("Done!\n")
# Try To Find Out How Many Rows Are In Result Set That Was Produced By The Query Just Executed
# (This Information Should Not Be Available)
try:
numRows = ibm_db.num_rows(preparedStmt)
except Exception:
pass
# Display An Appropriate Message, Based On The Information Returned
if numRows <= 0:
print("Unable to obtain information about the number of rows returned.\n")
else:
print("Number of rows returned by the query: " + str(numRows) + "\n")
# Free System Resources That Are Associated With The Prepared Statement And Result Set Produced
print("Freeing system resources associated with the prepared statement ... ", end="")
try:
returnCode = ibm_db.free_result(preparedStmt)
except Exception:
pass
# If The Appropriate System Resources Could Not Be Freed, Display An Error Message And Exit
if returnCode is False:
print("\nERROR: Unable to free the appropriate system resources.\n")
conn.closeConnection()
exit(-1)
# Otherwise, Complete The Status Message
else:
print("Done!\n")
# Create A Dictionary That Contains The Value Needed To Turn Row Prefetch Behavior On;
# This Enables Db2 To Determine The Number Of Rows That Are Returned By A Query (So The
# Entire Result Set Can Be Prefetched Into Memory, When Possible)
stmtOption = {ibm_db.SQL_ATTR_ROWCOUNT_PREFETCH : ibm_db.SQL_ROWCOUNT_PREFETCH_ON}
# Attempt To Set The Statement Option Specified
print("Turning SQL_ATTR_ROWCOUNT_PREFETCH behavior ON ... ", end="")
try:
returnCode = ibm_db.set_option(preparedStmt, stmtOption, 0)
except Exception:
pass
# If The Statement Option Could Not Be Set, Display An Error Message And Exit
if returnCode is False:
print("\nERROR: Unable to set the statement option specified.\n")
conn.closeConnection()
exit(-1)
# Otherwise, Complete The Status Message
else:
print("Done!\n")
# Execute The Prepared SQL Statement Again
print("Executing the prepared SQL statement again ... ", end="")
try:
resultSet = ibm_db.execute(preparedStmt)
except Exception:
pass
# If The SQL Statement Could Not Be Executed, Display An Error Message And Exit
if resultSet is False:
print("\nERROR: Unable to execute the SQL statement specified.")
conn.closeConnection()
exit(-1)
# Otherwise, Complete The Status Message
else:
print("Done!\n")
# Try To Find Out How Many Rows Are In Result Set That Was Produced By The Query Again
# (This Time, The Information Should Be Available)
try:
numRows = ibm_db.num_rows(preparedStmt)
except Exception:
pass
# Display An Appropriate Message, Based On The New Information Returned
if numRows <= 0:
print("Unable to obtain information about the number of rows returned.\n")
else:
print("Number of rows returned by the query: " + str(numRows) + "\n")
# Close The Database Connection That Was Opened Earlier
conn.closeConnection()
# Return Control To The Operating System
exit()