关于to_date()

源码：exec="SELECT round(SUM(N_FDL),2) FROM T_JHTJ_DAY_DLZB where c_plantid = '02' and d_date >= to_date(‘2008-01-01’,‘yyyy-mm-dd’) "
现在要将‘2008-01-01’变成每年的第一天，我写了sday=cstr(time1) + "-01-01"。可是
源码：exec="SELECT round(SUM(N_FDL),2) FROM T_JHTJ_DAY_DLZB where c_plantid = '02' and d_date >= to_date(sday,‘yyyy-mm-dd’) "语法不对，请指教。