LKS

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace belajar
{
    public partial class Form1 : Form
    {

        private SqlCommand cmd;
        private DataTable dt;
        private SqlDataAdapter sda;
        private SqlDataReader reader;

        connect konn = new connect();

        public Form1()
        {
            InitializeComponent();

            timer1.Start();


        }

        private void Form1_Load(object sender, EventArgs e)
        {
            SqlConnection conn = konn.GetConn();
            cmd = new SqlCommand("SELECT b.KodeBarang, u.Nama AS Name, j.Nama AS Job, b.NamaBarang, b.Jumlah, b.Harga FROM tbl_barang b JOIN tbl_User u ON b.IdUser = u.IdUser JOIN tbl_Job j ON b.IdJob = j.IdJob", conn);
            dt = new DataTable();
            sda = new SqlDataAdapter(cmd);
            sda.Fill(dt);
            dataGridView1.DataSource = dt;

            cmd = new SqlCommand("SELECT Nama FROM tbl_User", conn);
            conn.Open();
            reader = cmd.ExecuteReader();
            comboBox1.Items.Clear();

            while (reader.Read())
            {
                comboBox1.Items.Add(reader["Nama"].ToString());
            }
            conn.Close();

            cmd = new SqlCommand("SELECT Nama FROM tbl_Job", conn);
            conn.Open();
            reader = cmd.ExecuteReader();
            comboBox2.Items.Clear();

            while (reader.Read())
            {
                comboBox2.Items.Add(reader["Nama"].ToString());
            }
            conn.Close();

            dt.Columns.Add("Total harga", typeof(int));
            foreach (DataRow row in dt.Rows)
            {
                int Jumlah = Convert.ToInt32(row["Jumlah"]);
                int Harga = Convert.ToInt32(row["Harga"]);
                int total = Jumlah * Harga;
                row["Total Harga"] = total;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn = konn.GetConn();
            cmd = new SqlCommand("INSERT INTO tbl_Barang (KodeBarang, IdUser, IdJob, NamaBarang, Jumlah, Harga) SELECT @kode, u.IdUser, j.IdJob, @barang, @jumlah, @harga FROM tbl_User u, tbl_Job j WHERE u.Nama = @nama AND j.Nama = @job", conn);
            cmd.Parameters.AddWithValue("@kode", textBox1.Text);
            cmd.Parameters.AddWithValue("@nama", comboBox1.Text);
            cmd.Parameters.AddWithValue("@job", comboBox2.Text);
            cmd.Parameters.AddWithValue("@barang", textBox2.Text);
            cmd.Parameters.AddWithValue("@jumlah", textBox3.Text);
            cmd.Parameters.AddWithValue("@harga", textBox4.Text);
            conn.Open();
            cmd.ExecuteNonQuery();
            conn.Close();

            Form1_Load(this, null);
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            DateTime dt = DateTime.Now;
            this.label4.Text = dt.ToString();
        }
    }
}

SqlConnection conn = konn.GetConn();
cmd = new SqlCommand("UPDATE tbl_Barang SET NamaBarang = 'Barang Baru', Jumlah = 10 WHERE KodeBarang = @kode AND IdUser = (SELECT IdUser FROM tbl_User WHERE Nama = @nama) AND IdJob = (SELECT IdJob FROM tbl_Job WHERE Nama = @job)", conn);
cmd.Parameters.AddWithValue("@kode", textBox1.Text);
cmd.Parameters.AddWithValue("@nama", comboBox1.Text);
cmd.Parameters.AddWithValue("@job", comboBox2.Text);
conn.Open();
cmd.ExecuteNonQuery();
conn.Close();

Form1_Load(this, null);