对sql数据库非空输出的判断+从datagridview中读数据+多表联合sql语句

SELECT     TOP (200) AttendanceId, UserId, OnDutyTime, OffDutyTime, OverTimeStart, OverTimeEnd, RecordTime,
(CASE OverTimeStart WHEN '2000-01-01 00:00:00.000' THEN '未加班' ELSE OverTimeStart END) AS 加班了吗
FROM         AttendanceRecord

//显示申请加班并加班的记录
public DataTable selectOvertimeRecordTrue()
{
string sql = string.Format("SELECT OvertimeApply.NO, OvertimeApply.UserId, OvertimeApply.TrueName, OvertimeApply.AppDate, OvertimeApply.AddTime FROM OvertimeApply INNER JOIN AttendanceRecord ON OvertimeApply.UserId = AttendanceRecord.UserId AND OvertimeApply.AppDate = AttendanceRecord.RecordTime WHERE (OvertimeApply.State = 1) AND (AttendanceRecord.OverTimeStart <> '2000-01-01 00:00:00.000')");
DataConn conn = new DataConn(conStr);
ArrayList paramlist = new ArrayList();
IDataParameter[] param = (IDataParameter[])paramlist.ToArray(typeof(IDataParameter));
return conn.testDataTable(sql, param);
}