1. CompSci 280 S2 2107 Introduction to Software Development
MySQL Database Access

2. Today’s Agenda Topics: Reading: JDBC - MySQL Database Access
Introduction
Make a connection
Execute a SQL select statement
Python MySQL Database Access
Reading:
Download Connector/Python
Download Connector/J
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3. 1.JDBC Architecture Java code calls JDBC library. JDBC loads a driver
Driver talks to a particular database
Install the latest version of Connector/J.
Copying the driver to your computer, then adding the location of it to your class path.
Process any SQL statement with JDBC, follow these steps:
Establishing a connection
Create a statement
Execute the query
Process the ResultSet object
Close the connection.
Application
JDBC
Driver
Database
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4. 1.JDBC JDBC Object Classes
DriverManager
Loads, chooses drivers
Driver
connects to actual database
Connection
a series of SQL statements to and from the DB
Statement
a single SQL statement
ResultSet
the records returned from a Statement
DriverManager
Driver
Connection
Statement
ResultSet
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5. 1.JDBC Setting up Driver for MySQL
Steps:
Download Connector/J
Save the file either in the current directory or extension directory
Save the file in your current directory : C:\compsci280\ folder
1. Open Command prompt, type the following:
OR 2. Create a CLASSPATH variable in the Environment Variables
Save the file in extension folder
C:\Program Files\java\jre1.xxx > lib > ext
mysql-connector-java bin.jar
Either set the classpath or save the jar file in the ext folder
Set classpath= C:\compsci280\mysql-connector-java bin.jar;%CLASSPATH%
.;C:\compsci280\mysql-connector-java bin.jar\;
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6. 1.JDBC Establishing & Making a Connection
Before we can access data in a database, we must open a connection to the MySQL server.
Steps:
Loading the driver for MySQL Server database:
Class.forName(“xxxDriver”); // depends on the particular Driver
Making Connection
Connects to given JDBC URL with given user name and password
URL = “jdbc:mysql://host:3306/database_name”;
Returns a connection object
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection(URL, login, password);
Parameter
Description
host
studdb-mysql.fos.auckland.ac.nz
username
Your UPI
password
Password given from
Database name
stu_YOURUPI_COMPSCI_280_C_S2_2017
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7. 1.JDBC Example: TestConnection
Connection conn = null;
try {
Class.forName(JDBC_DRIVER);
System.out.println("... Driver loaded.");
conn = DriverManager.getConnection(URL, USER, PASS);
if (conn != null)
System.out.println("...MySQL Server connected.");
else
System.out.println("Failed to make connection!");
} catch (Exception e) {
System.out.println(e);
} finally {
conn.close();
} catch (Exception e) {}; }
If the output is:
java.sql.SQLException: No suitable driver found for …
Check the classpath if it has been set correctly.
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8. 1.JDBC Executing a Statement
A Statement object is used for executing a SQL statement and obtaining the results produced by it.
Steps:
Create a Statement Object
Execute the query
To execute a query, call an execute method from Statement:
ExecuteQuery: for select statements
Execute a SQL statement that returns a single ResultSet.
ExecuteUpdate: for insert/delete/update statements (extra)
Execute a SQL INSERT, UPDATE or DELETE statement. Returns the number of rows changed
stmt = con.createStatement();
sql = "SELECT * FROM EMPLOYEES";
rs = stmt.executeQuery(sql);
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9. 1.JDBC Result Set
A ResultSet provides access to a table of data generated by executing a Statement.
Only one ResultSet per Statement can be open at once.
The table rows are retrieved in sequence.
A ResultSet maintains a cursor pointing to its current row of data.
ResultSet Methods:
boolean next()
activates the next row
the first call to next() activates the first row
returns false if there are no more rows
void close()
disposes of the ResultSet
allows you to re-use the Statement that created it
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10. 1.JDBC ResultSet Methods
Type getType(int columnIndex)
returns the given field as the given type
fields indexed starting at 1 (not 0)
Type.INTEGER = 4
Type. FLOAT = 6
Type. CHAR= 1
int findColumn(String columnName)
looks up column index given column name
int getInt(int columnIndex)
double getDouble(int columnIndex)
String getString(int columnIndex)
Date getDate(int columnIndex)
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
String coffeeName = rs.getString("FIRST_NAME ");
... }
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11. 1.JDBC Example 2:
Count the number of employees in the EMPLOYEES table:
sql = "SELECT COUNT(*) FROM EMPLOYEES"
if (conn != null)
System.out.println("...MySQL Server connected.");
stmt = conn.createStatement();
rs = stmt.executeQuery(sql);
if (rs != null) {
while (rs.next())
System.out.println(rs.getInt(1)); } 10
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12. 1.JDBC Example 3:
Print last name and surname from the EMPLOYEES table:
sql = "SELECT FIRST_NAME, LAST_NAME FROM EMPLOYEES"
sql = "SELECT FIRST_NAME, LAST_NAME FROM EMPLOYEES"
...
stmt = conn.createStatement();
rs = stmt.executeQuery(sql);
if (rs != null) {
while (rs.next())
System.out.printf("%s, %s%n", rs.getString(1), rs.getString(2)); }
SUSAN, BROWN
JIM, KERN
MARTHA, WOODS
ELLEN, OWENS
HENRY, PERKINS
CAROL, ROSE
DAN, SMITH
FRED, CAMPBELL
PAULA, JACOBS
NANCY, HOFFMAN
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13. 2.Python MySQL Connector/Python
Commonly, Python applications will need to access a database of some sort.
The Python standard for database interfaces is the Python DB-API. Most Python database interfaces adhere to this standard.
You must download a separate DB API module for each database
MySQL alone has the following interface modules to choose:
MySQL for Python (import MySQLdb)
MySQL Connector/Python (import mysql.connector) etc
So which module do you choose? Well, as far as code-writing goes, it probably won’t make that much of a difference…
Download and install MySQL Connector/Python
mysql-connector-python py3.4-windows-x86-64bit.msi
Remember to check your Python version
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14. 2.Python Establishing & Making a Connection
Before we can access data in a database, we must open a connection to the MySQL server.
The connect() creates a connection to the MySQL server and returns a Connection object.
close() – close connection.
commit() – commit pending transaction (if supported).
rollback() – if supported by db, roll back to start of pending transaction.
cursor() – return a Cursor object for the connection.
import mysql.connector
...
conn = mysql.connector.connect(user=my_user, password=my_password, host=my_host, database=my_database)
Parameter
Description
host
studdb-mysql.fos.auckland.ac.nz
username
Your UPI
password
Password given from
Database name
stu_YOURUPI_COMPSCI_280_C_S2_2017
Use these information to connect to your own database
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15. 2.Python Creating Cursor object
Create a cursor object that allows Python code to execute database command.
They are bound to the connection for the entire lifetime and all the commands are executed in the context of the database session wrapped by the connection.
The following attributes should be available:
description – a description of the cursor with up to seven fields.
rowcount – number of rows produced by last execute method (-1 by default).
Methods:
close(): close the cursor object
cursor = conn.cursor()
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16. 2.Python Example 1 Steps: Connect the MySQL Database server
Create a cursor object
import mysql.connector
my_user = ""
my_password = ""
my_host = "studdb-mysql.fos.auckland.ac.nz"
my_database = "stu_kng001_COMPSCI_280_C_S2_2016"
try:
conn = mysql.connector.connect(user=my_user, password=my_password,
host=my_host, database=my_database)
cursor = conn.cursor()
print("Connected")
except:
print("Error: unable to fetch data")
cursor.close()
conn.close()
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17. 2.Python Executing a SQL Query
Execute sql queries using the execute() method associated with the cursor object.
Syntax:
prepare and execute an operation with parameters where the second argument may be a list of parameter sequences.
Examples: Count the number of employees in the EMPLOYEES table:
c.execute[many](op, [params])
sql = "SELECT COUNT(*) FROM EMPLOYEES“
conn = mysql.connector.connect(user=my_user, password=my_password,
host=my_host, database=my_database)
cursor = conn.cursor()
cursor.execute(sql)
result = cursor.fetchone()
print(result)
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18. 2.Python Fetch data from database
Multiple ways to retrieve data:
fetchall()
Fetch all (remaining) rows of a query result, returning them as a sequence of sequences (e.g. a list of tuples)
fetchmany(size)
Fetch the next set of rows of a query result, returning a sequence of sequences. It will return number of rows that matches to the size argument.
fetchone()
Fetch the next row of a query result set, returning a single sequence or None when no more data is available.
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19. 2.Python Example 3: One record: Multiple records:
Print the last name and surname from the EMPLOYEES table: 10
sql = "SELECT COUNT(*) FROM EMPLOYEES“
cursor.execute(sql)
result = cursor.fetchone()
print(result)
SUSAN, BROWN
JIM, KERN
MARTHA, WOODS
ELLEN, OWENS
HENRY, PERKINS
CAROL, ROSE
DAN, SMITH
FRED, CAMPBELL
PAULA, JACOBS
NANCY, HOFFMAN
cursor.execute(sql)
rows = cursor.fetchall()
for row in rows:
fname = row[0]
lname = row[1]
print( "%s, %s" % (fname, lname))
a list of tuples
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20. 2.JDBC Introduction What is JDBC?
A Java API Interface for database communication (created in 1995) – provide mechanism to allow Java Applets/Application access to database
JDBC = Java Database Connectivity
JDBC helps you to write Java applications that manage these three programming activities:
Connect to a data source, like a database
Send queries and update statements to the database
Retrieve and process the results received from the database in answer to your query
JDBC is implemented via classes in the java.sql package
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