JDBC statement + resultset introduction

JDBC-Statement

1. Statement The function of is to execute SQL sentence （ It will target different sql Statement executes different methods ）
   • perform DDL perhaps DML sentence ----》 The corresponding will execute int executeUpdate(String sql) Return to one int Type data , Indicates the affected row
   • perform DQL -----》 Corresponding to be executed ResultSet executeQuery（String sql） Return to one ResultSet object
   • explain :DDL ( Data definition language ) Common commands are creat drop alter Wait for the order
   • DML（ Data operation language ） Common commands are insert delete update
   • DQL（ Data query language ）select Return an object
   • Among them in DML And DDL There are differences. ：DML The return value must be >0, and DDL If the execution is successful, it may return 0. Try to use less in subsequent development DDL command

Case code

/** *  perform DML sentence  * @throws Exception */
@Test
public void testDML() throws  Exception {
    
    //1.  Registration drive 
    //Class.forName("com.mysql.jdbc.Driver");
    //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
    String url = "jdbc:mysql:///db1?useSSL=false";
    String username = "root";
    String password = "1234";
    Connection conn = DriverManager.getConnection(url, username, password);
    //3.  Definition sql
    String sql = "update account set money = 3000 where id = 1";
    //4.  Access to perform sql The object of  Statement
    Statement stmt = conn.createStatement();
    //5.  perform sql
    int count = stmt.executeUpdate(sql);// After execution DML sentence , Rows affected 
    //6.  Processing results 
    //System.out.println(count);
    if(count > 0){
    
        System.out.println(" Modification successful ~");
    }else{
    
        System.out.println(" Modification failed ~");
    }
    //7.  Release resources 
    stmt.close();
    conn.close();
}

/** 1.  perform DDL sentence  2. @throws Exception */
@Test
public void testDDL() throws  Exception {
    
    //1.  Registration drive 
    //Class.forName("com.mysql.jdbc.Driver");
    //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
    String url = "jdbc:mysql:///db1?useSSL=false";
    String username = "root";
    String password = "1234";
    Connection conn = DriverManager.getConnection(url, username, password);
    //3.  Definition sql
    String sql = "drop database db2";
    //4.  Access to perform sql The object of  Statement
    Statement stmt = conn.createStatement();
    //5.  perform sql
    int count = stmt.executeUpdate(sql);// After execution DDL sentence , May be 0
    //6.  Processing results 
    System.out.println(count);

    //7.  Release resources 
    stmt.close();
    conn.close();
}

JDBC-ResultSet

1. ResultSet（ Result set object ） The role of ：** Encapsulates the SQL The result of the query statement **
2. ResultSet Object provides methods for manipulating result data

boolean next()

• Move the cursor forward one line from the current position
• Judge whether the current line is a valid line

Method return value description ：

• true ： It works , There is data in the current row
• false ： Invalid line , There is no data in the current row

xxx getXxx( Parameters )： get data

• xxx : data type ; Such as ： int getInt( Parameters ) ;String getString( Parameters )
• Parameters
  • int Parameters of type ： Number of columns , from 1 Start
  • String Parameters of type ： Column name

Case code

/** *  perform DQL * @throws Exception */
@Test
public void testResultSet() throws  Exception {
    
    //1.  Registration drive 
    //Class.forName("com.mysql.jdbc.Driver");
    //2.  Get the connection ： If the connection is local mysql And the port is the default  3306  Can simplify writing 
    String url = "jdbc:mysql:///db1?useSSL=false";
    String username = "root";
    String password = "1234";
    Connection conn = DriverManager.getConnection(url, username, password);
    //3.  Definition sql
    String sql = "select * from account";
    //4.  obtain statement object 
    Statement stmt = conn.createStatement();
    //5.  perform sql
    ResultSet rs = stmt.executeQuery(sql);
    //6.  Processing results ,  Traverse rs All data in 
    /* // 6.1  Move the cursor down one line , And judge whether there is data in the current line  while (rs.next()){ //6.2  get data  getXxx() int id = rs.getInt(1); String name = rs.getString(2); double money = rs.getDouble(3); System.out.println(id); System.out.println(name); System.out.println(money); System.out.println("--------------"); }*/
    // 6.1  Move the cursor down one line , And judge whether there is data in the current line 
    while (rs.next()){
    
        //6.2  get data  getXxx()
        int id = rs.getInt("id");
        String name = rs.getString("name");
        double money = rs.getDouble("money");

        System.out.println(id);
        System.out.println(name);
        System.out.println(money);

        System.out.println("--------------");
    }

    //7.  Release resources 
    rs.close();
    stmt.close();
    conn.close();
}

end ！！！！！