Question

我正在为学校开展项目，我想使用COUNT（）函数。这是我的JDBC文件：

package jdbc;
import java.sql.*;

public class ForDataBase {

private Connection con;
        /**
          * constructor - create object con ( Connection type) 
          * invoking from the line: <jsp:useBean id="db" class = "jdbc.ForDataBase"/>
          */

    public ForDataBase(){ 
        try {
                       //we want use MySQL Connector
              Class.forName("com.mysql.jdbc.Driver").newInstance(); 

                        //param #1 - The URL of the database : jdbc:mysql://127.0.0.1:3306/kvutza1
                        // jdbc:mysql - protocol
                        // 127.0.0.1 - IP   
                        // 3306 - port number
                        // kvutza1 - database name
                       // param #2 -  default user of MySQLServer, name -root
                       // param #3 - root password
              con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/MyDB","root","1234");

        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
         /**
          * This function performs one direction SQL commands and returns
          * the number of updated rows
          */

    public int insertUpdateDelete(String sql){
        int num=0;
        try{
                 // Create object st (Statement type) - help object for con
            Statement st = con.createStatement();
                 // Invoke sql command
            num=st.executeUpdate(sql);
            st.close();
        } catch (SQLException e){
            e.printStackTrace();
        }   
        return num;
    }

        /**
          * This function performs Select SQL commands
          * and returns the result array of the data
          */

    public String [][] select(String sql){
        String result [][]=null;
        try{
            // Create object st (Statement type) - help object for con
                        Statement st = con.createStatement(
                              ResultSet.TYPE_SCROLL_INSENSITIVE,
                              ResultSet.CONCUR_UPDATABLE
                        );
                        // Invoke sql command and puts the result into ResultSet object - res
            ResultSet res = st.executeQuery(sql);
                        // m- the column number
            int m=res.getMetaData().getColumnCount();
                        // move the cursor to the last row
            res.last();
                        // n- the number of the last row
            int n=res.getRow();
                        // create the array
            result=new String[n][m];
                        // move the cursor before the first line
            res.beforeFirst();
                        // copy the data from resultset to the array
            int i=0;
            while (res.next())
            {

                for(int j=0;j<m;j++)
                    result[i][j]=res.getString(j+1);
                i++;
            }
            res.close();
            st.close();
        } catch (SQLException e){
            e.printStackTrace();
        }
        return result;
    }
}

你能帮我解决这个问题吗？我可以使用count（）函数吗？我的老师给了我这个档案，我根本不知道如何编辑他。

成功：

public int count(){
    int num=0;
    try{
        Statement st = con.createStatement();
        ResultSet rs3 = st.executeQuery("SELECT COUNT(*) AS count FROM users");
        while(rs3.next()){
            num = rs3.getInt("count");
        }
    } catch (SQLException e){
        e.printStackTrace();
    }   
    return num;
}

使用SQL COUNT（）jsp - JDBC

0 个答案: