想把下面sqlserver中的查询改成oracle中的写法，请问该怎么写？

Question

这是sqlserver中的：select Isnull(sum(isnull(ReceiveWeight,0)),0) as ReceiveWeight from t_Measurewhere Convert(char(10),MeasureDateTime,120) <='" + txtDates.Text.Trim() + "'这是我在oracle中写的：select nvl(sum(nvl(receiveweight,0)),0) as ReceiveWeight from t_Measurewhere Convert(varchar2(10),measure_Datetime,120) <='"+Date+"'

Answer 1

oracle里没有convert函数，varchar2转date类型的话用to_date函数，date类型转字符串用to_char函数。
to_date(String, 格式)，返回值是date类型
to_char(Date, 格式)，返回值是字符串
格式：
Year:
yy two digits 两位年 显示值:07
yyy three digits 三位年 显示值:007
yyyy four digits 四位年 显示值:2007

Month:
mm number 两位月 显示值:11
mon abbreviated 字符集表示 显示值:11月,若是英文版,显示nov
month spelled out 字符集表示 显示值:11月,若是英文版,显示november

Day:
dd number 当月第几天 显示值:02
ddd number 当年第几天 显示值:02
dy abbreviated 当周第几天简写 显示值:星期五,若是英文版,显示fri
day spelled out 当周第几天全写 显示值:星期五,若是英文版,显示friday
ddspth spelled out, ordinal twelfth

Hour:
hh two digits 12小时进制 显示值:01
hh24 two digits 24小时进制 显示值:13

Minute:
mi two digits 60进制 显示值:45

Second:
ss two digits 60进制 显示值:25

其它
Q digit 季度 显示值:4
WW digit 当年第几周 显示值:44
W digit 当月第几周 显示值:1

24小时格式下时间范围为： 0:00:00 - 23:59:59....
12小时格式下时间范围为： 1:00:00 - 12:59:59 ....

1. 日期和字符转换函数用法（to_date,to_char）

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual; //日期转化为字符串
select to_char(sysdate,'yyyy') as nowYear from dual; //获取时间的年
select to_char(sysdate,'mm') as nowMonth from dual; //获取时间的月
select to_char(sysdate,'dd') as nowDay from dual; //获取时间的日
select to_char(sysdate,'hh24') as nowHour from dual; //获取时间的时
select to_char(sysdate,'mi') as nowMinute from dual; //获取时间的分
select to_char(sysdate,'ss') as nowSecond from dual; //获取时间的秒

select to_date('2004-05-07 13:23:44','yyyy-mm-dd hh24:mi:ss') from dual//

Answer 2

select Nvl(Sum(Nvl(ReceiveWeight, 0)), 0) ReceiveWeight
from t_Measure
where To_Char(MeasureDateTime, 'yyyy-mm-dd') <= '" + txtDates.Text.Trim() + "'