C#中Excel数据导入到数据库中，部分代码不懂，请教大神们
 public void TransferData(string excelFile, string sheetName, string connectionString)
        {
            DataSet ds = new DataSet();
            try
            {
                //获取全部数据
                string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;" + "Data Source=" + excelFile + ";" + "Extended Properties = 'Excel 8.0;HDR=Yes;IMEX=1'";
                OleDbConnection conn = new OleDbConnection(strConn);
                conn.Open();
                string strExcel = "";
                OleDbDataAdapter myCommand = null;
                strExcel = string.Format("select * from [{0}$]", sheetName);
                myCommand = new OleDbDataAdapter(strExcel, strConn);
                myCommand.Fill(ds, sheetName);

                //如果目标表不存在则创建
                string strSql = string.Format("if object_id('{0}') is null create table {0}(", sheetName);
                foreach (System.Data.DataColumn c in ds.Tables[0].Columns)
                {
                    strSql += string.Format("[{0}] varchar(255),", c.ColumnName);
                }
                strSql = strSql.Trim(',') + ")";
                using (System.Data.SqlClient.SqlConnection sqlconn = new System.Data.SqlClient.SqlConnection(connectionString))
                {
                    sqlconn.Open();
                    System.Data.SqlClient.SqlCommand command = sqlconn.CreateCommand();
                    command.CommandText = s