Sql basics in java

Lesson: JDBC Basics

In this lesson you will learn the basics of the JDBC API.

• Getting Started sets up a basic database development environment and shows you how to compile and run the JDBC tutorial samples.
• Processing SQL Statements with JDBC outlines the steps required to process any SQL statement. The pages that follow describe these steps in more detail:
  • Establishing a Connection connects you to your database.
  • Connecting with DataSource Objects shows you how to connect to your database with DataSource objects, the preferred way of getting a connection to a data source.
  • Handling SQLExceptions shows you how to handle exceptions caused by database errors.
  • Setting Up Tables describes all the database tables used in the JDBC tutorial samples and how to create and populate tables with JDBC API and SQL scripts.
  • Retrieving and Modifying Values from Result Sets develop the process of configuring your database, sending queries, and retrieving data from your database.
  • Using Prepared Statements describes a more flexible way to create database queries.
  • Using Transactions shows you how to control when a database query is actually executed.
  • Using JdbcRowSet Objects
  • Using CachedRowSetObjets
  • Using JoinRowSet Objects
  • Using FilteredRowSet Objects
  • Using WebRowSet Objects
  • Using Large Objects
  • Using SQLXML Objects
  • Using Array Objects
  • Using DISTINCT Data Type
  • Using Structured Objects
  • Using Customized Type Mappings
  • Using Datalink Objects
  • Using RowId Objects

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  Lesson: JDBC Basics

  In this lesson you will learn the basics of the JDBC API.

  • Getting Started sets up a basic database development environment and shows you how to compile and run the JDBC tutorial samples.
  • Processing SQL Statements with JDBC outlines the steps required to process any SQL statement. The pages that follow describe these steps in more detail:
    • Establishing a Connection connects you to your database.
    • Connecting with DataSource Objects shows you how to connect to your database with DataSource objects, the preferred way of getting a connection to a data source.
    • Handling SQLExceptions shows you how to handle exceptions caused by database errors.
    • Setting Up Tables describes all the database tables used in the JDBC tutorial samples and how to create and populate tables with JDBC API and SQL scripts.
    • Retrieving and Modifying Values from Result Sets develop the process of configuring your database, sending queries, and retrieving data from your database.
    • Using Prepared Statements describes a more flexible way to create database queries.
    • Using Transactions shows you how to control when a database query is actually executed.
    • Using JdbcRowSet Objects
    • Using CachedRowSetObjets
    • Using JoinRowSet Objects
    • Using FilteredRowSet Objects
    • Using WebRowSet Objects
    • Using Large Objects
    • Using SQLXML Objects
    • Using Array Objects
    • Using DISTINCT Data Type
    • Using Structured Objects
    • Using Customized Type Mappings
    • Using Datalink Objects
    • Using RowId Objects

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    Processing SQL Statements with JDBC

    In general, to process any SQL statement with JDBC, you follow these steps:

    This page uses the following method, CoffeesTable.viewTable , from the tutorial sample to demonstrate these steps. This method outputs the contents of the table COFFEES . This method will be discussed in more detail later in this tutorial:

    public static void viewTable(Connection con) throws SQLException < String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES"; try (Statement stmt = con.createStatement()) < ResultSet rs = stmt.executeQuery(query); while (rs.next()) < String coffeeName = rs.getString("COF_NAME"); int supplierID = rs.getInt("SUP_ID"); float price = rs.getFloat("PRICE"); int sales = rs.getInt("SALES"); int total = rs.getInt("TOTAL"); System.out.println(coffeeName + ", " + supplierID + ", " + price + ", " + sales + ", " + total); >> catch (SQLException e) < JDBCTutorialUtilities.printSQLException(e); >>

    Establishing Connections

    First, establish a connection with the data source you want to use. A data source can be a DBMS, a legacy file system, or some other source of data with a corresponding JDBC driver. This connection is represented by a Connection object. See Establishing a Connection for more information.

    Creating Statements

    A Statement is an interface that represents a SQL statement. You execute Statement objects, and they generate ResultSet objects, which is a table of data representing a database result set. You need a Connection object to create a Statement object.

    For example, CoffeesTable.viewTable creates a Statement object with the following code:

    There are three different kinds of statements:

    • Statement : Used to implement simple SQL statements with no parameters.
    • PreparedStatement : (Extends Statement .) Used for precompiling SQL statements that might contain input parameters. See Using Prepared Statements for more information.
    • CallableStatement: (Extends PreparedStatement .) Used to execute stored procedures that may contain both input and output parameters. See Stored Procedures for more information.

    Executing Queries

    To execute a query, call an execute method from Statement such as the following:

    • execute : Returns true if the first object that the query returns is a ResultSet object. Use this method if the query could return one or more ResultSet objects. Retrieve the ResultSet objects returned from the query by repeatedly calling Statement.getResultSet .
    • executeQuery : Returns one ResultSet object.
    • executeUpdate : Returns an integer representing the number of rows affected by the SQL statement. Use this method if you are using INSERT , DELETE , or UPDATE SQL statements.

    For example, CoffeesTable.viewTable executed a Statement object with the following code:

    ResultSet rs = stmt.executeQuery(query);

    Processing ResultSet Objects

    You access the data in a ResultSet object through a cursor. Note that this cursor is not a database cursor. This cursor is a pointer that points to one row of data in the ResultSet object. Initially, the cursor is positioned before the first row. You call various methods defined in the ResultSet object to move the cursor.

    For example, CoffeesTable.viewTable repeatedly calls the method ResultSet.next to move the cursor forward by one row. Every time it calls next , the method outputs the data in the row where the cursor is currently positioned:

    ResultSet rs = stmt.executeQuery(query); while (rs.next()) < String coffeeName = rs.getString("COF_NAME"); int supplierID = rs.getInt("SUP_ID"); float price = rs.getFloat("PRICE"); int sales = rs.getInt("SALES"); int total = rs.getInt("TOTAL"); System.out.println(coffeeName + ", " + supplierID + ", " + price + ", " + sales + ", " + total); >// .

    Closing Connections

    When you are finished using a Connection , Statement , or ResultSet object, call its close method to immediately release the resources it’s using.

    Alternatively, use a try -with-resources statement to automatically close Connection , Statement , and ResultSet objects, regardless of whether an SQLException has been thrown. (JDBC throws an SQLException when it encounters an error during an interaction with a data source. See Handling SQL Exceptions for more information.) An automatic resource statement consists of a try statement and one or more declared resources. For example, the CoffeesTable.viewTable method automatically closes its Statement object, as follows:

    public static void viewTable(Connection con) throws SQLException < String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES"; try (Statement stmt = con.createStatement()) < ResultSet rs = stmt.executeQuery(query); while (rs.next()) < String coffeeName = rs.getString("COF_NAME"); int supplierID = rs.getInt("SUP_ID"); float price = rs.getFloat("PRICE"); int sales = rs.getInt("SALES"); int total = rs.getInt("TOTAL"); System.out.println(coffeeName + ", " + supplierID + ", " + price + ", " + sales + ", " + total); >> catch (SQLException e) < JDBCTutorialUtilities.printSQLException(e); >>

    The following statement is a try -with-resources statement, which declares one resource, stmt , that will be automatically closed when the try block terminates:

    try (Statement stmt = con.createStatement()) < // . >

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