JDBC Select Count example

In this tutorial  we will learn how work COUNT()  in query with mysql JDBC driver. This tutorial  COUNT(*)  returns a count of the number of rows retrieved, whether or not they contain NULL values. Table of user :

Mysql query  "SELECT COUNT(*) FROM user"  count  number of rows,  whether or not they contain  NULL values. So this query count number  of  rows 5. If  change the COUNT(*) to COUNT(user_name)  then count number of rows 4 that contain user_name  it  ignore the  user_name  (NULL) value . The code of  "SelectCount.java" is:

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.SQLException;
import java.sql.ResultSet;
  
public class SelectCount{
 // JDBC driver name and database URL
 static String driverName = "com.mysql.jdbc.Driver";
 static String url = "jdbc:mysql://localhost:3306/";

 // defined and set value in  dbName, userName and password variables
 static String dbName = "testjdbc";
 static String userName = "root";
 static String password = "";
	
 public static void main(String[] args){
	// create Connection con, and Statement stmt 
	Connection con=null;
	Statement stmt=null;
	try{
		Class.forName(driverName).newInstance();
		con = DriverManager.getConnection(url+dbName, userName, password);
		try{
			stmt = con.createStatement();
			String query = "SELECT COUNT(*) FROM user";
			ResultSet rs=stmt.executeQuery(query);			
			//Extact result from ResultSet rs
			while(rs.next()){
			    System.out.println("COUNT(*)="+rs.getInt("COUNT(*)"));				
			  }
			// close ResultSet rs
			rs.close();
		   } catch(SQLException s){						
				s.printStackTrace();
			 }
		// close Connection and Statement
		con.close();
		stmt.close();
		}catch (Exception e){
			e.printStackTrace();
		 }
  }
}

Program Output :

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