将某个日期以前的记录删除的语句该怎么写？

我想删除表borrowinfo中用户输入的某一个日期以前的所有记录。表中有一个日期时间型字段returndate,怎么写？
date=request.form("date")
sql="delete borrowinfo where returndate......"
set rs=conn.execute(sql)
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dates=request.form("date")
delete borrowinfo where datediff('s',returndate,'"&dates&"')>0
set rs=conn.execute(sql)

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dates=request("date")
sql="delete borrowinfo where datediff(s,returndate,'"&dates&"')>0"
conn.execute sql

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dates=request.form("date")

sql="delete from borrowinfo where returndate <'"&date()&"'"
set rs=conn.execute(sql)