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Chapter 23 Relational Databases. CHAPTER GOALS To learn how to query a database with the Structured Query Language (SQL) To connect to databases with.

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Presentation on theme: "Chapter 23 Relational Databases. CHAPTER GOALS To learn how to query a database with the Structured Query Language (SQL) To connect to databases with."— Presentation transcript:

1 Chapter 23 Relational Databases

2 CHAPTER GOALS To learn how to query a database with the Structured Query Language (SQL) To connect to databases with Java Database Connectivity (JDBC) To write database programs that insert, update, and query data in a relational database

3 Relational Database Stores information in tables Each table column has a name and data type

4 Product Table in a Relational Database

5 Product Table Each row corresponds to a product Column headers correspond to attributes of the product All items in the same column are the same data type

6 SQL SQL stands for Structured Query Language SQL is a command language for interacting with databases Most relational databases follow the SQL standard Some SQL commands o QUERY o CREATE TABLE o INSERT o DROP TABLE

7 Some SQL Types and Their Corresponding Java Types previousprevious | start | nextstartnext File Purse.java previousprevious | start | nextstartnext

8 SQL to Create a Table CREATE TABLE Products { Product_Code CHAR(11) Description CHAR(40) Unit_Price DECIMAL(10,2) }

9 SQL to Add Data to a Database Use the INSERT command to insert rows into the table Issue one command for each row of the table INSERT INTO Products VALUES (' ', 'Hair dryer', 29.95)

10 Linking Tables Replicating the same data in multiple rows has two problems It is wasteful to store the same information multiple times If the data needs to change it has to be changed in multiple places Instead you should distribute the data over multiple tables

11 Poor Design for an Invoice Table with Replicated Customer Data

12 Two Tables for Invoice and Customer Data

13 Linking Tables In the table above, customer data are not replicated Customer table contains a single record for each customer Invoice table has no customer data The two tables are linked by the Customer_Number field The customer number is a unique identifier

14 Linking Tables Primary key is a column (or combination of columns) whose value uniquely specifies a table record Foreign key is a reference to a primary key in a linked table Foreign keys need not be unique

15 Implementing One-to-Many Relationships Each invoice may have many items Do not replicate columns, one for each item Do distribute the information in two tables, invoice and item Link each item to its invoice with an Invoice_Number foreign key in the item table previousprevious | start | nextstartnext previousprevious | start | nextstartnext

16 Poor Design for Invoice Table with Replicated Columns

17 Linked Invoice and Item Tables

18 Sample Database

19 Queries Once the database is constructed, we can query it for information o What are the names and addresses of all customers? o What are the names and addresses of all customers who live in California? o What are the names and addresses of all customers who buy toasters? o What are the names and addresses of all customers with unpaid invoices ?

20 Simple Query Use the SQL SELECT statement to query a database The query to select all data from the Customer table: SELECT * FROM customer The outcome of a query is a view A view is a "window" through which you can see some of the database

21 Selecting Columns You may want to view only some of the columns in the table The query to select the city and state of all customers from the Customer table: SELECT City, State FROM Customer

22 Selecting Subsets You can select rows that fit a particular criteria When you want to select a subset, use the WHERE clause The query to find all customers in California: SELECT * FROM Customer WHERE State = 'CA' The query to select all customers NOT in California SELECT * FROM Customer WHERE State <> 'CA'

23 Result of SELECT * FROM Customer WHERE State = 'CA'

24 Selecting Subsets You can match patterns with LIKE The right-hand side is a string that can contain special characters o Special symbol _ matches exactly one character o Special symbol % matches any character sequence The expression to match all Name strings whose second character is an "o": Name LIKE '_o%'

25 Selecting Subsets You can combine expressions with logical connectives AND, OR, NOT SELECT * FROM Product WHERE Price < 100 AND Description <> 'Toaster' You can select both row and column subsets SELECT Name, City FROM Customer WHERE State = 'CA'

26 Calculations Use the count function to find out how many customers there are in California SELECT COUNT(*) FROM Customer WHERE State = 'CA' The * means you want to calculate whole records Other functions are SUM, AVG, MAX, MIN These functions must access a specific column. Put the column name in parentheses SELECT AVG(Price) FROM Product

27 Joins The information you want may be spread over multiple tables Use Product.Product_Code to specify the Product_Code column in the Product table Use Item.Product_Code to specify the Product_Code column in the Item table To select all invoices that include a car vacuum SELECT Item.Invoice_Number FROM Product, Item WHERE Product.Description = 'Car vacuum' AND Product.Product_Code = Item.Product_Code

28 Joins A query that involves multiple tables is a join When using a join, do these things List all tables that are involved in the query in the FROM clause Use the TableName.ColumnName syntax to refer to column names List all join conditions in the WHERE clause (TableName1.ColumnName1 = TableName2.ColumnName2)

29 Updating and Deleting Data The DELETE and UPDATE commands modify the database The DELETE command deletes rows To delete all customers in California DELETE FROM Customer WHERE State = 'CA'

30 Updating and Deleting Data The UPDATE query lets you update columns of all records that fulfill a certain condition To add one to the quantity of every item in invoice number UPDATE Item SET Quantity = Quantity + 1 WHERE Invoice_Number = '11731' Both UPDATE and DELETE return the number of rows updated or deleted

31 File TestDB.java 01: import java.sql.Connection; 02: import java.sql.ResultSet; 03: import java.sql.Statement; 04: 05: /** 06: Tests a database installation by creating and querying 07: a sample table. Call this program as 08: java -classpath driver_class_path;. TestDB database.properties 09: */ 10: public class TestDB 11: { 12: public static void main(String[] args) throws Exception 13: { 14: if (args.length == 0) 15: { 16: System.out.println( 17: "Usage: TestDB propertiesFile"); 18: System.exit(0); 19: }

32 20: else 21: SimpleDataSource.init(args[0]); 22: 23: Connection conn = SimpleDataSource.getConnection(); 24: 25: Statement stat = conn.createStatement(); 26: 27: stat.execute("CREATE TABLE Test (Name CHAR(20))"); 28: stat.execute("INSERT INTO Test VALUES ('Romeo')"); 29: 30: ResultSet result = stat.executeQuery("SELECT * FROM Test"); 31: result.next(); 32: System.out.println(result.getString("Name")); 33: result.close(); 34: 35: stat.execute("DROP TABLE Test"); 36: 37: stat.close(); 38: conn.close(); 39: } 40: }

33 File SimpleDataSource.java 01: import java.sql.Connection; 02: import java.sql.DriverManager; 03: import java.sql.SQLException; 04: import java.io.FileInputStream; 05: import java.io.IOException; 06: import java.util.Properties; 07: 08: /** 09: A simple data source for getting database connections. 10: */ 11: public class SimpleDataSource 12: { 13: /** 14: Initializes the data source. fileName the name of the property file that 16: contains the database driver, url, username and password 17: */ 18: public static void init(String fileName)

34 19: throws IOException, ClassNotFoundException 20: { 21: Properties props = new Properties(); 22: FileInputStream in = new FileInputStream(fileName); 23: props.load(in); 24: 25: String driver = props.getProperty("jdbc.driver"); 26: url = props.getProperty("jdbc.url"); 27: String username = props.getProperty("jdbc.username"); 28: String password = props.getProperty("jdbc.password"); 29: 30: Class.forName(driver); 31: } 32: 33: /** 34: Gets a connection to the database. the database connection 36: */

35 37: public static Connection getConnection() throws SQLException 38: { 39: return DriverManager.getConnection(url, 40: username, password); 41: } 42: 43: private static String url; 44: private static String username; 45: private static String password; 46: } 47: 48: 49: 50: 51: 52: 53: 54: 55: 56: 57:

36 File database.properties 1: jdbc.driver=COM.cloudscape.core.JDBCDriver 2: jdbc.url=jdbc:cloudscape:bigjava;create=true 3: jdbc.username= 4: jdbc.password=

37 Connecting to the DataBase Use a Connection object to access a database from a Java program Load the database driver Ask the DriverManager for a connection When you are done, close the database connection String driver =...; String url =...; String username =...; String password =...; Class.forName(driver); //load driver Connection conn = DeviceManager.getConnection(url, username, password); //database commands conn.close();

38 Connecting to the Database Decouple connection management from the other database code You can use the SimpleDataSource class to do this Call its static init method with the name of the database configuration file Configuration file is a text file containing four lines o jdbc.driver =... o jdbc.url =... o jdbc.username =... o jdbc.password =...

39 Connecting to the Database The init method uses the Properties class to read the file Properties class has a load method to read a file of key/value pairs from a stream Properties props = new Properties(); FileInputStream in = new FileInputStream(fileName); props.load(in); The getProperty method returns the value of a given key String driver = props.getProperty("jdbc.driver"); Now when you need a connection call Connection conn = SimpleDataSource.getConnection();

40 Executing SQL Statements A Connection object can create Statement objects Statement stat = conn.createStatement(); The execute method of the Statement class executes a SQL statement stat.execute("CREATE TABLE Test (Name CHAR(20))") stat.execute("INSERT INTO Test VALUES ('Romeo')") Use executeQuery method of the Statement class to issue a query String queryStatement = "SELECT * FROM Test"; ResultSet result = stat.executeQuery(queryStatement); The result of a SQL query is returned in a ResultSet object

41 Executing SQL Statements Use the executeUpdate method of the Statement class to execute a UPDATE statement The method returns the number of rows effected String updateStatement = "UPDATE Item“ + "SET Quantity = Quantity + 1" + "WHERE Invoice_Number = '11731'"; int count = stat.executeUpdate(updateStatement);

42 Executing SQL Statements You can also use a generic execute statement to execute queries It returns a boolean value to indicate whether the SQL command yields a result set If there is a result set, you can get it with the getResultSet method If there is no result set, you can get the update count with the getUpdateCount method String command =... ; boolean hasResultSet = stat.execute(command); if (hasResultSet) { ResultSet result = stat.getResultSet();... { else { int count = stat.getUpdateCount();... }

43 Executing SQL Statements You can reuse a Statement object to execute new SQL commands Each Statement object should only have one active ResultSet If you need to look at multiple result sets at the same time, create multiple Statement objects Close the current ResultSet before issuing a new query on the same statement result.close(); When you are done with a Statement object, close it That will also close the ResultSet stat.close();

44 Analyzing Query Results Use the next method of the ResultSet to iterate through the query results a row at a time When a result set is first returned from an executeQuery, no row data are available Use the next method to move to the first row The next method returns a boolean value indicating whether more rows of data are available while (result.next()) { //inspect column data from the current row }

45 Analyzing Query Results To get the column values from a row, use one of the various get methods There are two get methods for each type of data (string, integer, double...) One uses an integer parameter that indicates the column position Column positions start at 1 String productCode = result.getString(1);

46 Analyzing Query Results import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; /** A server that executes the Simple Bank Access Protocol. */ public class BankServer { public static void main(String[] args ) throws IOException { final int ACCOUNTS_LENGTH = 10; Bank bank = new Bank(ACCOUNTS_LENGTH); final int SBAP_PORT = 8888; ServerSocket server = new ServerSocket(SBAP_PORT); System.out.println("Waiting for clients to connect..."); import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; /** A server that executes the Simple Bank Access Protocol. */ public class BankServer { public static void main(String[] args ) throws IOException { final int ACCOUNTS_LENGTH = 10; Bank bank = new Bank(ACCOUNTS_LENGTH); final int SBAP_PORT = 8888; ServerSocket server = new ServerSocket(SBAP_PORT); System.out.println("Waiting for clients to connect..."); The other type of get method uses a string parameter for the column name String productCode = result.getString("Product_Code"); Use getInt to fetch an integer column value int quantity = result.getInt("Quantity"); Use getDouble to fetch an double column value double unitPrice = result.getDouble("Price");

47 Result Set Meta Data Result set meta data describes the properties of the result set Use the ResultSetMetaData class to find out the column names in an unknown table You can get the meta data object form the result set ResultSetMetaData metaData = result.getMetaData();

48 Result Set Meta Data Use getColumnCount method to get the number of columns Use getColumnLabel method to get the name of each column Use getColumnDisplay Size method to get the column width for (int i = 1) i <= metaData.getColumnCount(); i++) { String columnName = metaData.getColumnLabel(i); int columnSize = metaData.getColumnDisplaySize(i);... }

49 Result Set Meta Data The following program reads a file containing SQL statements and executes them If there is a result set, the result set is printed Meta data from the result set is used to determine the column count and column label Run the program as java ExecSQL database.properties product.sql Or interactively as java ExecSQL database.properties

50 File cityzone.sql 1: CREATE TABLE CityZone (City CHAR(30), Zone CHAR(45)) 2: INSERT INTO CityZone VALUES ('San Francisco', 'America/Los_Angeles') 3: INSERT INTO CityZone VALUES ('Kaoshiung', 'Asia/Taipei') 4: SELECT * FROM CityZone

51 File ExecSQL.java 001: import java.net.*; 002: import java.sql.*; 003: import java.io.*; 004: import java.util.*; 005: 006: class ExecSQL 007: { 008: /** 009: Executes all SQL statements in a file args 011: 012: args[0]: the property file for the database connection 013: args[1]: the file with SQL statements 014: 015: */ 016: public static void main (String args[]) 017: {

52 018: try 019: { 020: if (args.length == 0) 021: { 022: System.out.println 023: ("Usage: ExecSQL propertyFile [statementFile]"); 024: System.exit(0); 025: } 026: Connection con = getConnection(args[0]); 027: Statement stmt = con.createStatement(); 028: 029: 030: String tableName = ""; 031: 032: Reader reader; 033: if (args.length > 1) 034: reader = new FileReader(args[1]); 035: else 036: reader = new InputStreamReader(System.in); 037: BufferedReader in = new BufferedReader(reader);

53 038: 039: 040: String line; 041: while ((line = in.readLine()) != null) 042: { 043: boolean hasResultSet = stmt.execute(line); 044: if (hasResultSet) 045: showResultSet(stmt); 046: } 047: 048: in.close(); 049: stmt.close(); 050: con.close(); 051: } 052: catch (SQLException ex) 053: { 054: System.out.println ("SQLException:"); 055: while (ex != null) 056: { 057: System.out.println ("SQLState: "

54 058: + ex.getSQLState()); 059: System.out.println ("Message: " 060: + ex.getMessage()); 061: System.out.println ("Vendor: " 062: + ex.getErrorCode()); 063: ex = ex.getNextException(); 064: System.out.println (""); 065: } 066: } 067: catch (IOException ex) 068: { 069: System.out.println("IOException: " + ex); 070: ex.printStackTrace (); 071: } 072: } 073: 074: /** 075: Opens a database connection fileName the name of the property file that contains the 077: database driver, url, username and password

55 the connection to the database 079: */ 080: public static Connection getConnection(String fileName) 081: throws SQLException, IOException 082: { 083: Properties props = new Properties(); 084: FileInputStream in = new FileInputStream(fileName); 085: props.load(in); 086: 087: String drivers = props.getProperty("jdbc.drivers"); 088: if (drivers != null) 089: System.setProperty("jdbc.drivers", drivers); 090: String url = props.getProperty("jdbc.url"); 091: String username = props.getProperty("jdbc.username"); 092: String password = props.getProperty("jdbc.password"); 093: 094: return 095: DriverManager.getConnection(url, username, password); 096: } 097:

56 098: public static void showResultSet(Statement stmt) 099: throws SQLException 100: { 101: ResultSet rs = stmt.getResultSet(); 102: ResultSetMetaData rsmd = rs.getMetaData(); 103: int columnCount = rsmd.getColumnCount(); 104: while (rs.next()) 105: { 106: for (int i = 1; i <= columnCount; i++) 107: { 108: if (i > 1) System.out.print(", "); 109: System.out.print(rs.getString(i)); 110: } 111: System.out.println(); 112: } 113: rs.close(); 114: } 115: }

57 Case Study: A Bank Database This is a reimplementation of the ATMSimulation In the simulation each customer has a customer number, a PIN, a checking account and a savings account The data will be stored in two tables in a database

58 Tables for ATMSimulation

59 Case Study: A Bank Database The Bank class needs to connect to the database whenever it is asked to find a customer Its find method oConnects to the database oSelects the customer with the given account number oVerifies the PIN oCreates an customer object from the database information

60 Case Study: A Bank Database public Customer find(int customerNumber, int pin) throws SQLException { Customer c = null; Connection conn = SimpleDataSource.getConnection(); Statement stat = conn.createStatement(); ResultSet result = stat.executeQuery("SELECT *" + " FROM Customer WHERE Customer_Number = " + customerNumber);

61 if (result.next() && pin == result.getInt("PIN")) c = new Customer(customerNumber, result.getInt("Checking_Account_Number"), result.getInt("Savings_Account_Number")); result.close(); stat.close(); conn.close(); return c; }

62 Case Study: A Bank Database The BankAccount methods are different now The getBalance method gets the balance from the data base The withdraw and deposit methods update the database immediately

63 File ATMSimulation.java 01: import javax.swing.JFrame; 02: 03: /** 04: A simulation of an automatic teller machine 05: */ 06: public class ATMSimulation 07: { 08: public static void main(String[] args) 09: { 10: if (args.length == 0) 11: { 12: System.out.println( 13: "Usage: ATMSimulation propertiesFile"); 14: System.exit(0); 15: } 16: else

64 17: { 18: try 19: { 20: SimpleDataSource.init(args[0]); 21: } 22: catch (Exception ex) 23: { 24: ex.printStackTrace(); 25: System.exit(0); 26: } 27: } 28: 29: JFrame frame = new ATM(); 30: frame.setTitle("First National Bank of Java"); 31: frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 32: frame.pack(); 33: frame.show(); 34: } 35: }

65 File ATM.java 001: import java.awt.Container; 002: import java.awt.FlowLayout; 003: import java.awt.GridLayout; 004: import java.awt.event.ActionEvent; 005: import java.awt.event.ActionListener; 006: import java.io.FileInputStream; 007: import java.io.IOException; 008: import java.sql.SQLException; 009: import java.util.Properties; 010: import javax.swing.JButton; 011: import javax.swing.JFrame; 012: import javax.swing.JOptionPane; 013: import javax.swing.JPanel; 014: import javax.swing.JTextArea; 015: 016: /** 017: A frame displaying the components of an ATM

66 018: */ 019: class ATM extends JFrame 020: { 021: /** 022: Constructs the user interface of the ATM application. 023: */ 024: public ATM() 025: { 026: theBank = new Bank(); 027: 028: // construct components 029: 030: pad = new KeyPad(); 031: 032: display = new JTextArea(4, 20); 033: 034: aButton = new JButton(" A "); 035: aButton.addActionListener(new AButtonListener()); 036: 037: bButton = new JButton(" B ");

67 038: bButton.addActionListener(new BButtonListener()); 039: 040: cButton = new JButton(" C "); 041: cButton.addActionListener(new CButtonListener()); 042: 043: // add components to content pane 044: 045: JPanel buttonPanel = new JPanel(); 046: buttonPanel.setLayout(new GridLayout(3, 1)); 047: buttonPanel.add(aButton); 048: buttonPanel.add(bButton); 049: buttonPanel.add(cButton); 050: 051: Container contentPane = getContentPane(); 052: contentPane.setLayout(new FlowLayout()); 053: contentPane.add(pad); 054: contentPane.add(display); 055: contentPane.add(buttonPanel); 056: try 057: {

68 058: setNextState(START_STATE); 059: } 060: catch (SQLException exception) 061: { 062: JOptionPane.showMessageDialog(null, 063: exception.getMessage()); 064: } 065: } 066: 067: /** 068: Sets the current customer number to the keypad value 069: and sets state to PIN. 070: */ 071: public void setCustomerNumber() throws SQLException 072: { 073: customerNumber = (int)pad.getValue(); 074: setNextState(PIN_STATE); 075: } 076: 077: /**

69 078: Gets PIN from keypad, finds customer in bank. 079: If found sets state to ACCOUNT, else to START. 080: */ 081: public void selectCustomer() throws SQLException 082: { 083: int pin = (int)pad.getValue(); 084: currentCustomer 085: = theBank.find(customerNumber, pin); 086: if (currentCustomer == null) 087: setNextState(START_STATE); 088: else 089: setNextState(ACCOUNT_STATE); 090: } 091: 092: /** 093: Sets current account to checking or savings. Sets 094: state to TRANSACT account one of CHECKING_ACCOUNT or SAVINGS_ACCOUNT 096: */ 097: public void selectAccount(int account) throws SQLException

70 098: { 099: if (account == CHECKING_ACCOUNT) 100: currentAccount 101: = currentCustomer.getCheckingAccount(); 102: else 103: currentAccount 104: = currentCustomer.getSavingsAccount(); 105: setNextState(TRANSACT_STATE); 106: } 107: 108: /** 109: Withdraws amount typed in keypad from current account. 110: Sets state to ACCOUNT. 111: */ 112: public void withdraw() throws SQLException 113: { 114: currentAccount.withdraw(pad.getValue()); 115: setNextState(ACCOUNT_STATE); 116: } 117:

71 118: /** 119: Deposits amount typed in keypad to current account. 120: Sets state to ACCOUNT. 121: */ 122: public void deposit() throws SQLException 123: { 124: currentAccount.deposit(pad.getValue()); 125: setNextState(ACCOUNT_STATE); 126: } 127: 128: /** 129: Sets state and updates display message. state the next state 131: */ 132: public void setNextState(int newState) 133: throws SQLException 134: { 135: state = newState; 136: pad.clear(); 137: if (state == START_STATE)

72 138: display.setText("Enter customer number\nA = OK"); 139: else if (state == PIN_STATE) 140: display.setText("Enter PIN\nA = OK"); 141: else if (state == ACCOUNT_STATE) 142: display.setText("Select Account\n" 143: + "A = Checking\nB = Savings\nC = Exit"); 144: else if (state == TRANSACT_STATE) 145: display.setText("Balance = " 146: + currentAccount.getBalance() 147: + "\nEnter amount and select transaction\n" 148: + "A = Withdraw\nB = Deposit\nC = Cancel"); 149: } 150: 151: private class AButtonListener implements ActionListener 152: { 153: public void actionPerformed(ActionEvent event) 154: { 155: try 156: { 157: if (state == START_STATE)

73 158: setCustomerNumber(); 159: else if (state == PIN_STATE) 160: selectCustomer(); 161: else if (state == ACCOUNT_STATE) 162: selectAccount(CHECKING_ACCOUNT); 163: else if (state == TRANSACT_STATE) 164: withdraw(); 165: } 166: catch (SQLException exception) 167: { 168: JOptionPane.showMessageDialog(null, 169: exception.getMessage()); 170: } 171: } 172: } 173: 174: private class BButtonListener implements ActionListener 175: { 176: public void actionPerformed(ActionEvent event) 177: {

74 178: try 179: { 180: if (state == ACCOUNT_STATE) 181: selectAccount(SAVINGS_ACCOUNT); 182: else if (state == TRANSACT_STATE) 183: deposit(); 184: } 185: catch (SQLException exception) 186: { 187: JOptionPane.showMessageDialog(null, 188: exception.getMessage()); 189: } 190: } 191: } 192: 193: private class CButtonListener implements ActionListener 194: { 195: public void actionPerformed(ActionEvent event) 196: { 197: try

75 198: { 199: if (state == ACCOUNT_STATE) 200: setNextState(START_STATE); 201: else if (state == TRANSACT_STATE) 202: setNextState(ACCOUNT_STATE); 203: } 204: catch (SQLException exception) 205: { 206: JOptionPane.showMessageDialog(null, 207: exception.getMessage()); 208: } 209: } 210: } 211: 212: private int state; 213: private int customerNumber; 214: private Bank theBank; 215: private Customer currentCustomer; 216: private BankAccount currentAccount; 217:

76 218: private JButton aButton; 219: private JButton bButton; 220: private JButton cButton; 221: 222: private KeyPad pad; 223: private JTextArea display; 224: 225: private static final int START_STATE = 1; 226: private static final int PIN_STATE = 2; 227: private static final int ACCOUNT_STATE = 3; 228: private static final int TRANSACT_STATE = 4; 229: 230: private static final int CHECKING_ACCOUNT = 1; 231: private static final int SAVINGS_ACCOUNT = 2; 232: }

77 File Bank.java 01: import java.sql.Connection; 02: import java.sql.ResultSet; 03: import java.sql.Statement; 04: import java.sql.SQLException; 05: 06: /** 07: A bank consisting of multiple bank accounts. 08: */ 09: public class Bank 10: { 11: /** 12: Finds a customer with a given number and PIN. conn the database connection customerNumber the customer number pin the personal identification number the matching customer, or null if none found 17: */

78 18: public Customer find(int customerNumber, int pin) 19: throws SQLException 20: { 21: Customer c = null; 22: Connection conn = SimpleDataSource.getConnection(); 23: Statement stat = conn.createStatement(); 24: ResultSet result = stat.executeQuery("SELECT *" 25: + " FROM Customer WHERE Customer_Number = " 26: + customerNumber); 27: 28: if (result.next() && pin == result.getInt("PIN")) 29: c = new Customer(customerNumber, 30: result.getInt("Checking_Account_Number"), 31: result.getInt("Savings_Account_Number")); 32: result.close(); 33: stat.close(); 34: conn.close(); 35: return c; 36: } 37: }

79 File BankAccount.java 01: import java.sql.Connection; 02: import java.sql.ResultSet; 03: import java.sql.Statement; 04: import java.sql.SQLException; 05: 06: /** 07: A bank account has a balance that can be changed by 08: deposits and withdrawals. 09: */ 10: public class BankAccount 11: { 12: /** 13: Constructs a bank account with a given balance. anAccountNumber the account number 15: */ 16: public BankAccount(int anAccountNumber) 17: {

80 18: accountNumber = anAccountNumber; 19: } 20: 21: /** 22: Deposits money into a bank account. accountNumber the account number amount the amount to deposit 25: */ 26: public void deposit(double amount) 27: throws SQLException 28: { 29: Connection conn = SimpleDataSource.getConnection(); 30: Statement stat = conn.createStatement(); 31: stat.execute("UPDATE Account" 32: + " SET Balance = Balance + " + amount 33: + " WHERE Account_Number = " + accountNumber); 34: stat.close(); 35: conn.close(); 36: } 37:

81 38: /** 39: Withdraws money from a bank account. accountNumber the account number amount the amount to withdraw 42: */ 43: public void withdraw(double amount) 44: throws SQLException 45: { 46: Connection conn = SimpleDataSource.getConnection(); 47: Statement stat = conn.createStatement(); 48: stat.execute("UPDATE Account" 49: + " SET Balance = Balance - " + amount 50: + " WHERE Account_Number = " + accountNumber); 51: stat.close(); 52: conn.close(); 53: } 54: 55: /** 56: Gets the balance of a bank account. accountNumber the account number

82 the account balance 59: */ 60: public double getBalance() 61: throws SQLException 62: { 63: double balance = 0; 64: Connection conn = SimpleDataSource.getConnection(); 65: Statement stat = conn.createStatement(); 66: ResultSet result = stat.executeQuery("SELECT Balance" 67: + " FROM Account WHERE Account_Number = " 68: + accountNumber); 69: if (result.next()) 70: balance = result.getDouble(1); 71: result.close(); 72: stat.close(); 73: conn.close(); 74: return balance; 75: } 76: 77: private int accountNumber; 78: }

83 File Customer.java 01: /** 02: A bank customer with a checking and savings account. 03: */ 04: public class Customer 05: { 06: /** 07: Constructs a customer with a given number and PIN. aCustomerNumber the customer number checkingAccountNumber the checking account number savingsAccountNumber the savings account number 11: */ 12: public Customer(int aCustomerNumber, 13: int checkingAccountNumber, int savingsAccountNumber) 14: { 15: customerNumber = aCustomerNumber; 16: checkingAccount = new BankAccount(checkingAccountNumber); 17: savingsAccount = new BankAccount(savingsAccountNumber);

84 18: } 19: 20: /** 21: Gets the checking account of this customer. the checking account 23: */ 24: public BankAccount getCheckingAccount() 25: { 26: return checkingAccount; 27: } 28: 29: /** 30: Gets the savings account of this customer. the checking account 32: */ 33: public BankAccount getSavingsAccount() 34: { 35: return savingsAccount; 36: } 37:

85 38: private int customerNumber; 39: private BankAccount checkingAccount; 40: private BankAccount savingsAccount; 41: }

86 Transactions A transaction is a set of database updates that should either succeed in their entirety or not happen at all If you transfer money from one account to another, you want both the withdraw and deposit to happen or neither Use COMMIT and ROLLBACK commands to manage transactions To transfer money from one account to another UPDATE Account SET Balance = Balance WHERE Account_Number = ' ' UPDATE Account SET Balance = Balance WHERE Account_Number = ' ' COMMIT

87 Transactions COMMIT makes the updates permanent ROLLBACK command undoes all changes up to the last COMMIT By default, the JDBC library commits all database updates For transaction processing, turn off autocommit mode Connection conn... ; conn.setAutoCommit(false); Statement stat = conn.getStatement();

88 Transactions Issue the updates that form the transaction then call the commit method of the Statement class stat.executeUpdate( "UPDATE Account SET Balance = Balance -" + amount + " WHERE Account_Number = " +fromAccount); stat.executeUpdate( “ UPDATE Account SET Balance = Balance +" + amount + " WHERE Account_Number = " +toAccount); COMMIT If you encounter an error, call the rollback method This is usually done in an exception handler try {... } catch(SQLException exception) { stat.rollback(); }

89 Scrollable and Updatable Result Sets Because the result set of a query may be very large, the ResultSet object does not contain the entire result set It is a gateway to a result set stored in the database Each time you call next a single row is transferred into the ResultSet object The user may want to look back at previous row. Use a scrollable result set to do this

90 Scrollable and Updatable Result Sets To get a scrollable result set, you first need to create a Statement object with its type and concurrency parameters set with constants from the ResultSet class Statement stat = conn.createStatement(ResultSet.TYPE_SROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY); ResultSet result = stat.executeQuery(... );

91 Scrollable and Updatable Result Sets Possible type constants o TYPE_SCROLL_SENSITIVE  Result set scrollable  Result set is updated when other processes change the information in the database o TYPE_SCROLL_INSENSITIVE  Result set scrollable  Result set is NOT updated when other processes change the information in the database oTYPE_FORWARD_ONLY  Result set not scrollable  This is the default

92 Possible concurrency constants o CONCUR_UPDATABLE  You can update the database by editing the result set o CONCUR_READ_ONLY  You can NOT update the database by editing the result set

93 Scrollable and Updatable Result Sets Methods for navigating a scrollable result set o previous() - moves to the previous row o first() and last() - moves to first or last row o relative(n) - moves by n rows o absolute(n) - moves to row number n A scrollable result set effectively gives you random access to the result set

94 Updatable Result Sets An updatable result set makes it easy to modify the contents of a database without using SQL commands Create a statement Statement stat = conn.createStatement( ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE); Get a result set String accountQuery = "SELECT * WHERE Account_Number = " + account; ResultSet result = stat.executeQuery(accountQuery);

95 Get the value from the Balance column double balance = result.getDouble("Balance"); Update the balance in the current row, but not in the database result.updateDouble("Balance", balance + deposit); Change the data in the database result.updateRow()

96 Updatable Result Sets Use an updatable result set to insert new rows Move the cursor to a special position called the insert row Update all column values Call updateRow method result.moveToInsertRow(); result.updateString("Account_Number"," "); result.updateString("Customer_Number","992345"); result.updateDouble("Balance",1000); result.updateRow();

97 Speeding Queries Up Indexing Prepared statements Stored procedures

98 Indexing If a table has a primary key, the database can build an index file Index file stores information on how to access a row quickly when its primary key is given If the primary key is a single column, you can tag the column with the keyword PRIMARY KEY CREATE TABLE Products ( Product_Code CHAR(10) PRIMARY KEY, Description CHAR(40), Price DECIMAL(10,2) ) A table index can speed up database queries

99 Prepared Statements Use a prepared statement for frequently repeated database queries and updates When you send a prepared statement to a database o The database formulates a query strategy o Saves it with the prepared statement

100 Prepared Statements To prepare a query to get the bank account information for a given account String query = "SELECT * WHERE Account_Number = ?"; PreparedStatement prepStat = conn.prepareStatement(query); The ? denotes variables that you fill in when you make an actual query Use the set method to set the variables prepStat.setString(1,accountNumber); When you have all variables set, call the executeQuery method ResultSet result = prepStat.executeQuery();

101 Stored Procedures Are executed in the database kernel This is much faster than issuing sequences of SQL commands Databases don't all use the same syntax for stored procedures You must first download the stored procedure into the database You can use the CREATE PROCEDURE statement to do this

102 Stored Procedures A procedure for transferring money from one account to another CREATE PROCEDURE transfer( :from INTEGER, :to INTEGER, :amount DECIMAL(10,2) BEGIN UPDATE Accounts SET Balance = Balance - :amount WHERE Account_Number = :from; UPDATE Accounts SET Balance = Balance + :amount WHERE Account_Number = :to; END

103 In Java, download a stored procedure by executing SQL statement that defines the procedure String definition = "CREATE PROCEDURE transfer(" ") BEGIN" "END"; stat.execute(definition);

104 Stored Procedures To call the stored procedure, use the CallableStatement class You get a CallableStatement from the prepareCall method of the Connection class The { } tell the JDBC driver that the call is not standard SQL and needs to be translated into the syntax of this database CallableStatement callStat = conn.prepareCall( "{call transfer(?,?,?)});

105 You need to set values in the ? placeholders before calling the procedure callStat.setInt(1, fromAccount); callStat.setInt(2, toAccount); callStat.setDouble(3, amount); Call the procedure callStat.execute();


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