I need to prevent inserting duplicated records in a sql table and if exists show message says already exists
this is my button event :
private void button2_Click(object sender, EventArgs e)
{
conn.Open();
com.Connection = conn;
sql = "INSERT INTO lapusers([username],[fillingcode],[branch],[department],[agency])VALUES(@username,@fillingcode,@branch,@department,@agency)";
com.CommandText = sql;
com.Parameters.Clear();
com.Parameters.AddWithValue("@username", userlapbox.Text);
com.Parameters.AddWithValue("@fillingcode", userfilllapbox.Text);
com.Parameters.AddWithValue("@branch", comboBox2.Text);
com.Parameters.AddWithValue("@department", comboBox1.Text);
com.Parameters.AddWithValue("@agency", comboBox3.Text);
com.ExecuteNonQuery();
MessageBox.Show("Created Successfully ..");
conn.Close();
}