To get the "today" value in SQL:
convert(date, GETDATE())
To get "yesterday":
DATEADD(day, -1, convert(date, GETDATE()))
To get "today minus X days": change the -1 into -X.
So for all yesterday's rows, you get:
select * from tablename
where date >= DATEADD(day, -1, convert(date, GETDATE()))
and date < convert(date, GETDATE())