Executing Sql Commands
- 1. Basic JDBC Programming Concepts
- 2. Database URLs For databases on the Internet/intranet, the subname can contain the Net URL //hostname:port/… The < subprotocol > can be any name that a database understands. The odbc subprotocol name is reserved for ODBC-style data sources. A normal ODBC database JDBC URL looks like: jdbc:odbc:<>;User=<>;PW=<> jdbc:postgresql ://www.hcmuaf.edu.vn/ts
- 3. Making the Connection Loading a driver: Class.forName(className) Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); System.setProperty(“jdbc.drivers”, “className”); System.setProperty(“jdbc.drivers”, “sun.jdbc.odbc.JdbcOdbcDriver”); Making a connection Connection conn = DriverManager.getConnection(…); static Connection getConnection(String url); static Connection getConnection(String url, String user,String password); static int getLoginTimeout(); // seconds static void setLoginTimeout(int seconds); static void println(String message);// in ra logfile static void registerDriver(Driver d); static void deregisterDriver(Driver d);
- 4. Executing SQL Commands The Statement object does all of the work to interact with the Database Management System in terms of SQL statements. You can create many Statement objects from one Connection object. JDBC supports three types of statements: Statement : the SQL is prepared and executed in one step (from the application program point of view) PreparedStatement : the driver stores the execution plan handle for later use (SQL command with a parameters). CallableStatement : the SQL statement is actually making a call to a stored procedure The Connection object has the createStatement (), prepareStatement (), and prepareCall () methods to create these Statement objects.
- 5. Creating and Using Direct SQL Statements A Statement object is created using the createStatement () method in the Connection object obtained from the call to DriverManager.getConnection resultSet executeQuery (String sql) int executeUpdate (String sql) boolean execute(String sql) The executeUpdate method can execute actions such as INSERT , UPDATE , and DELETE as well as data definition commands such as CREATE TABLE , and DROPTABLE . The executeUpdate method returns a count of the rows that were affected by the SQL command. The executeQuery method is used to execute SELECT queries. The executeQuery object returns an object of type ResultSet that you use to walk through the result a row at a time. ResultSet rs = stat.executeQuery("SELECT * FROM Books")
- 6. Using executeUpdate method try { Class. forName ( "sun.jdbc.odbc.JdbcOdbcDriver" ); Connection connection = DriverManager . getConnection (url,userName,password); Statement statement = connection.createStatement(); String sqlCommand = "CREATE TABLE Books(Title CHAR(60)," + "ISBN CHAR(13),Price CURRENCY)" ; statement.executeUpdate (sqlCommand); sqlCommand = " INSERT INTO Books VALUES(" + "'Beyond HTML', '0-07-882198-3', 27.95)" ; statement.executeUpdate (sqlCommand); statement.close (); connection.close (); } catch (Exception e) { System. out .println( e.getMessage() ); }
- 7. Using executeQuery method try { Class. forName ( "sun.jdbc.odbc.JdbcOdbcDriver" ); Connection connection = DriverManager. getConnection (url, userName,password); Statement statement = connection.createStatement(); String sqlCommand = "SELECT * FROM BOOKS" ; ResultSet rs = statement.executeQuery(sqlCommand); while (rs.next()) { String title = rs.getString(1); String isbn = rs.getString(2); float price = rs.getFloat( "Price" ); System. out .println(title + ", " + isbn + " , " + price); } rs.close(); } catch (Exception e){};
- 8. SQL data types and corresponding Java types java.sql.Time TIME java.sql.Date DATE Boolean BOOLEAN String VARCHAR( n ) String CHARACTER( n ) or CHAR( n ) double DOUBLE float REAL double FLOAT(n) java.sql.Numeric NUMERIC( m,n ), DECIMAL( m,n )or DEC( m,n ) short SMALLINT int INTEGER or INT Java data type SQL data type
- 9. Creating and Using PreparedStatement The PreparedStatement , the driver actually sends only the execution plan ID and the parameters to the DBMS. This results in less network traffic and is well-suited for Java applications on the Internet. The PreparedStatement should be used when you need to execute the SQL statement many times in a Java application . The DBMS discards the execution plan at the end of the program. So, the DBMS must go through all of the steps of creating an execution plan every time the program runs. The PreparedStatement object achieves faster SQL execution performance than the simple Statement object , as the DBMS does not have to run through the steps of creating the execution plan. Notice that the executeQuery (), executeUpdate (), and execute () methods do not take any parameters. Return Type Method Name Parameter ResultSet executeQuery ( ) int executeUpdate ( ) Boolean execute ( )
- 10. Creating and Using PreparedStatement One of the major features of a PreparedStatement is that it can handle IN types of parameters . The parameters are indicated in a SQL statement by placing the ? as the parameter marker instead of the actual values. In the Java program, the association is made to the parameters with the setXXXX () methods. All of the setXXXX () methods take the parameter index, which is 1 for the first " ? ," 2 for the second " ? ,"and so on. void setBoolean (int parameterIndex, boolean x) void setByte (int parameterIndex, byte x) void setDouble (int parameterIndex, double x) void setFloat (int parameterIndex, float x) void setInt (int parameterIndex, int x) void setLong (int parameterIndex, long x) void setNumeric (int parameterIndex, Numeric x) void setShort (int parameterIndex, short x) void setString (int parameterIndex, String x)
- 11. Creating and Using PreparedStatement try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Connection connection = DriverManager.getConnection(url,userName,password); PrepStmt = connection.prepareStatement("SELECT * FROM BOOKS WHERE ISBN = ? "); PrepStmt.setString(1,"0-07-882198-3"); ResultSet rs = PrepStmt.executeQuery () ; while (rs.next()) { title = rs.getString(1); isbn = rs.getString(2); price = rs.getFloat("Price"); System.out.println(title + ", " + isbn + " , " + price ); } rs.close(); PrepStmt.close(); connection.close(); }
- 12. java.sql.DriverManager static Connection getConnection(String url, String user,String password) establishes a connection to the given database and returns a Connection object.
- 13. java.sql.Connection Statement createStatement() creates a statement object that can be used to execute SQL queries and updates without parameters. PreparedStatement prepareStatement(String sql ) returns a PreparedStatement object containing the precompiled statement. The string sql contains a SQL statement that can contain one or more parameter placeholders denoted by ? characters. void close() immediately closes the current connection.
- 14. java.sql.Statement ResultSet executeQuery(String sql) executes the SQL statement given in the string and returns a ResultSet to view the query result. int executeUpdate(String sql) executes the SQL INSERT , UPDATE , or DELETE statement specified by the string. Also used to execute Data Definition Language (DDL) statements such as CREATE TABLE . Returns the number of records affected, or -1 for a statement without an update count. boolean execute(String sql) executes the SQL statement specified by the string. Returns true if the statement returns a result set, false otherwise. Use the getResultSet or getUpdateCount method to obtain the statement outcome. int getUpdateCount() Returns the number of records affected by the preceding update statement, or -1 if the preceding statement was a statement without an update count. Call this method only once per executed statement. ResultSet getResultSet() Returns the result set of the preceding query statement, or null if the preceding statement did not have a result set. Call this method only once per executed statement.
- 15. java.sql.ResultSet boolean next() makes the current row in the result set move forward by one. Returns false after the last row. Note that you must call this method to advance to the first row. xxx getXxx(int columnNumber) xxx getXxx(String columnName) ( xxx is a type such as int , double , String , Date , etc.) return the value of the column with column index columnNumber or with column names, converted to the specified type. Not all type conversions are legal. See documentation for details. int findColumn(String columnName) gives the column index associated with a column name. void close() immediately closes the current result set.
- 16. java.sql.PreparedStatement void set Xxx (int n, Xxx x) ( Xxx is a type such as int , double , String , Date , etc.) sets the value of the n-th parameter to x . void clearParameters() clears all current parameters in the prepared statement. ResultSet executeQuery() executes a prepared SQL query and returns a ResultSet object. int executeUpdate() executes the prepared SQL INSERT , UPDATE , or DELETE statement represented by the PreparedStatement object. Returns the number of rows affected, or 0 for DDL statements.