在Java JDBC中查找rowcount的正确方法

Question

我尝试过不同的方法来获取java JDBC中的行数,但似乎没有给出正确的结果.我做的有什么不对吗？

即使customer表为空,我应该将rowcount设为0,我也不明白为什么我得到一个非零行数值.

方法1 -

query = "SELECT * FROM customer WHERE username ='"+username+"'";
rs = stmt.executeQuery(query);
ResultSetMetaData metaData = rs.getMetaData();
rowcount = metaData.getColumnCount();

方法2 -

query = "SELECT * FROM customer WHERE username ='"+username+"'";
rs = stmt.executeQuery(query);
rowcount = rs.last() ? rs.getRow() : 0;

Answer 1

看到这段代码:

import java.io.*;
import java.sql.*;

public class CountRows{
    public static void main(String[] args) {
        System.out.println("Count number of rows in a specific table!");
        Connection con = null;
        int count = 0;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctutorial","root","root");
            try {
                Statement st = con.createStatement();
                BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("Enter table name:");
                String table = bf.readLine();
                ResultSet res = st.executeQuery("SELECT COUNT(*) FROM "+table);
                while (res.next()){
                    count = res.getInt(1);
                }
                System.out.println("Number of row:"+count);
            }
            catch (SQLException s){
                System.out.println("SQL statement is not executed!");
            }
        }
        catch (Exception e){
            e.printStackTrace();
        }
    }
}