oracle sql语句传变量nvl((select sum(NETWEIGHT) from ST_WEIGHTETL

oracle sql语句传变量
nvl((select sum(NETWEIGHT)
from ST_WEIGHTETL jl, ST_FUELCOMMDATA ab
where jl.DATANUM = ab.datanum
and jl.siteid = ab.siteid
and jl.orgid = ab.orgid
and ab.WEIGHTR_STATUS = '已确认'
and to_char(ab.WEIGHTTIME, 'yyyy-mm-dd') =

to_char(sysdate,'yyyy-mm-dd')
and ab.COMPANYNUM = ss.COMPANYNUM
and ab.YEARPLANTYPE = ss.YEARPLANTYPE),
0) as 日进煤量
nvl((select sum(NETWEIGHT)
from ST_WEIGHTETL jl, ST_FUELCOMMDATA ab
where jl.DATANUM = ab.datanum
and jl.siteid = ab.siteid
and jl.orgid = ab.orgid
and ab.WEIGHTR_STATUS = '已确认'
and to_char(ab.WEIGHTTIME, 'yyyy-mm') =
to_char(sysdate,'yyyy-mm')
and ab.COMPANYNUM = ss.COMPANYNUM
and ab.YEARPLANTYPE = ss.YEARPLANTYPE),
0) as 月进煤累计
如何把查询中设计到的系统时间的判断to_char(sysdate,'yyyy-mm-dd')换成一个时间类型的变量
急!