Code:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Data.OleDb;
using System.Data.SqlClient;
using System.Data.SqlServerCe;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public sealed class SQL
    {
        public static string CreateConnectionString(string server, string username, string password, string database)
        {
            int timeout = 10;
            server = (server != null && server.Length > 0 ? "Data Source=" + server + ";" : "Data Source=(local);");
            string login = "Integrated Security=SSPI;";
            if(username != null && username.Length > 0) {
                if(password != null && password.Length > 0)
                    login = "User ID=" + username + ";Password=" + password + ";";
                else
                    login = "User ID=" + username + ";Password=\"\";";
            }
            string catalog = "Initial Catalog=" + (database != null && database.Length > 0 ? database : "master");
            return server + login + catalog + (timeout > 0 ? ";Connect Timeout=10" : "");
        }

        public static string CreateConnectionString(string fileName, string password)
        {
            if(!string.IsNullOrEmpty(fileName)) {
                string cs = "Data Source=" + fileName;
                if(password != null && password.Length > 0) cs += ";Password=" + password + ";";
                return cs;
            }
            return "";
        }

        public static ConnectionStringType GetConnectionStringType(string connectionString)
        {
            if(!string.IsNullOrEmpty(connectionString)) {
                string connectionStringLower = connectionString.ToLower();
                if(connectionStringLower.Contains(".sdf")) return ConnectionStringType.SqlServerCe;
                if(connectionStringLower.Contains(".mdb")) return ConnectionStringType.Access;
                return ConnectionStringType.SqlServer;
            }
            return ConnectionStringType.None;
        }

        public static DbConnection GetConnection(string connectionString)
        {
            switch(GetConnectionStringType(connectionString)) {
                case ConnectionStringType.SqlServer:
                    return new SqlConnection(connectionString);
                case ConnectionStringType.SqlServerCe:
                    return new SqlCeConnection(connectionString);
                case ConnectionStringType.Access:
                    return new OleDbConnection(connectionString);
            }
            return null;
        }

        public static DbDataAdapter GetDataAdapter(string connectionString, string query)
        {
            switch(GetConnectionStringType(connectionString)) {
                case ConnectionStringType.SqlServer:
                    return new SqlDataAdapter(query, connectionString);
                case ConnectionStringType.SqlServerCe:
                    return new SqlCeDataAdapter(query, connectionString);
                case ConnectionStringType.Access:
                    return new OleDbDataAdapter(query, connectionString);
            }
            return null;
        }

        public static DbCommand GetCommand(string connectionString, string query)
        {
            DbConnection connection = GetConnection(connectionString);
            if(connection != null) {
                switch(GetConnectionStringType(connectionString)) {
                    case ConnectionStringType.SqlServer:
                        return new SqlCommand(query, connection as SqlConnection);
                    case ConnectionStringType.SqlServerCe:
                        return new SqlCeCommand(query, connection as SqlCeConnection);
                    case ConnectionStringType.Access:
                        return new OleDbCommand(query, connection as OleDbConnection);
                }
            }
            return null;
        }

        public static DataTable ExecuteQuery(string connectionString, string query)
        {
            DataTable dataTable = new DataTable();
            DbDataAdapter adapter = null;
            try {
                adapter = GetDataAdapter(connectionString, query);
                if(adapter != null) adapter.Fill(dataTable);
            } catch(Exception ex) {
                MessageBox.Show(ex.Message, "", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            if(adapter != null) try { adapter.Dispose(); } catch { }
            return dataTable;
        }

        public static int ExecuteNonQuery(string connectionString, string statement)
        {
            if(!string.IsNullOrEmpty(statement)) {
                DbConnection con = null;
                DbCommand cmd = null;
                int result = -1;
                try {
                    con = GetConnection(connectionString);
                    con.Open();
                    cmd = con.CreateCommand();
                    cmd.CommandText = statement;
                    result = cmd.ExecuteNonQuery();
                } catch(Exception ex) {
                    MessageBox.Show(ex.Message, "", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                if(cmd != null) try { cmd.Dispose(); } catch { }
                if(con != null) try { con.Close(); con.Dispose(); } catch { }
                return result;
            }
            return 0;
        }


        public static void DisplayDataTable(DataTable table)
        {
            Form form = new Form();
            DataGridView grid = new DataGridView();
            grid.DataSource = table;
            grid.Dock = DockStyle.Fill;
            form.Controls.Add(grid);
            form.Size = new Size(800, 600);
            form.StartPosition = FormStartPosition.CenterScreen;
            form.ShowDialog();
            grid.Dispose();
            form.Dispose();
        }
        
    }

    public enum ConnectionStringType
    {
        None,
        SqlServer,
        SqlServerCe,
        Access
    }
}

Code:

            string connectionString = SQL.CreateConnectionString("", "", "", "PROBA");
            DataTable dataTable = SQL.ExecuteQuery(connectionString, "select * from dbo.sysobjects"); 
            SQL.DisplayDataTable(dataTable);