Add, delete, modify and query the database

After we have connected to the database earlier,It is necessary to perform further operations on the database,The simplest is to add, delete, modify and check operations

1.查

 public void QueeyAll() throws Exception{
    
        Class.forName(driver);
        conn = DriverManager.getConnection(url,user,password);
        stmt = conn.createStatement();

        String sql = "select * from product";
        result = stmt.executeQuery(sql);

        while(result.next()){
    
            int proid = result.getInt("proid");
            String proname = result.getString("proname");
            String proflag = result.getString("proflag");
            double procost = result.getDouble("procost");
            System.out.print(proid + "\t");
            System.out.print(proname + "\t");
            System.out.print(proflag + "\t");
            System.out.print(procost + "\n");
        }

        result.close();
        stmt.close();
        conn.close();
    }

We return data from the database by defining a result set.

2.增

public int InsertPro(int proid,String proname,double procost,String proflag) throws Exception{
    
        Class.forName(driver);
        conn = DriverManager.getConnection(url,user,password);
        stmt = conn.createStatement();

        String sql = "insert into product (proid,proname,procost,proflag) values(null,?,?,?)";
        PreparedStatement preparedStatement = conn.prepareStatement(sql);

        preparedStatement.setString(1,proname);
        preparedStatement.setDouble(2,procost);
        preparedStatement.setString(3,proflag);

        int i = preparedStatement.executeUpdate();
        System.out.println(i);
        return i;
    }

Determine whether the insertion is successful by defining the number of affected rows

3.删

public int DeleteByID(int proID) throws Exception{
    

        Class.forName(driver);
        conn = DriverManager.getConnection(url,user,password);

        String sql = "delete from product where proid = ?";

        PreparedStatement preparedStatement = conn.prepareStatement(sql);
        preparedStatement.setInt(1,proID);

        //Output the number of affected rows to determine whether the deletion is successful
        int i = preparedStatement.executeUpdate();
        System.out.println(i);

        preparedStatement.close();
        conn.close();

        return i;
    }

Deleting is the same as adding,It also determines whether the deletion is successful by defining the number of affected rows

4.改

public int UpdatePro(int proid,String proname,double procost,String proflag) throws Exception{
    
        Class.forName(driver);
        conn = DriverManager.getConnection(url,user,password);
        stmt = conn.createStatement();

        String sql = "update product set proname = ? , procost = ? ,proflag = ? where proid = ?";
        PreparedStatement preparedStatement = conn.prepareStatement(sql);

        preparedStatement.setString(1, proname);
        preparedStatement.setDouble(2, procost);
        preparedStatement.setString(3, proflag);
        preparedStatement.setInt(4, proid);

        int i = preparedStatement.executeUpdate();
        System.out.println(i);

        return i;

5.小结

It should be noted that the order of parameter indices should correspond one-to-one