//拷贝时请注意文件的定义名称要一致

namespace DAL
{
    public class SQLHelper
    {
        //定义一个连接字符串
        string connstr = ConfigurationManager.ConnectionStrings["Constr"].ConnectionString;

        #region 执行非查询语句，返回受影响的行数
        /// <summary>
        /// 执行非查询语句，返回受影响的行数
        /// </summary>
        /// <param name="sql"></param>
        /// <param name="ct"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public int ExecuteNonQuery(string sql, CommandType ct, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.CommandType = ct;
                    foreach (SqlParameter parameter in parameters)
                    {
                        cmd.Parameters.Add(parameter);
                    }
                    return cmd.ExecuteNonQuery();
                }
            }
        }
        #endregion

        #region 执行sql语句，返回第一行第一列的值
       
       
        /// <summary>
        /// 执行SQL语句，返回第一行第一列的值，因为不知道类型，所以用Object
        /// </summary>
        /// <param name="sql"></param>
        /// <param name="ct"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public object ExecuteScalar(string sql, CommandType ct, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.CommandType = ct;
                    foreach (SqlParameter parameter in parameters)
                    {
                        cmd.Parameters.Add(parameter);
                    }
                    return cmd.ExecuteScalar();
                }
            }
        }
        #endregion

        #region 执行sql语句，返回一个表
        /// <summary>
        /// 执行sql语句，返回一个表
        /// </summary>
        /// <param name="sql"></param>
        /// <param name="ct"></param>
        /// <param name="parameters"></param>
        /// <returns></returns>
        public DataTable ExecuteDataTable(string sql, CommandType ct, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.CommandType = ct;
                    foreach (SqlParameter parameter in parameters)
                    {

                        cmd.Parameters.Add(parameter);
                    }
                    DataSet ds = new DataSet();
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    adapter.Fill(ds);
                    return ds.Tables[0];
                }
            }
        }
        #endregion
    }
}

Sql Server助手类