SQL Server 2012: compare and subtract dates in join

Question

I want to get the results of this join query which are in the last 30 days.

V.[4501001] contains the nvarchar dates in this format dd/mm/yyyy

Here is my query:

(select Distinct T.PId from [dbo].[TrialStatus] T inner join 
    form.TP_VISDATE V on T.pid = V.pid
    where T.cid = 1064 and T.sid = 300 and (Convert(NVARCHAR, V.[4501001], 103) < Convert(NVARCHAR,GETDATE(),103)) and (Convert(NVARCHAR, V.[4501001], 103) > DATEADD(DD,-30,Convert(NVARCHAR,GETDATE(),103))))

If I use Convert(NVARCHAR,GETDATE(),103) I get false results because this

select DATEADD(Day,-30,Convert(NVARCHAR,GETDATE(),103))

returns 2018-01-08 00:00:00.000 instead of the day 30 days before today

But if I use GETDATE() as is without conversion I get this error:

The conversion of a nvarchar data type to a datetime data type resulted in an out-of-range value.

Answer 1

Convert the value to a date, not a string!

select Distinct T.PId
from [dbo].[TrialStatus] T inner join 
     form.TP_VISDATE V 
     on T.pid = V.pid
where T.cid = 1064 and
      T.sid = 300 and
      Convert(date, V.[4501001], 103) < Convert(date, GETDATE()) and
      Convert(date, V.[4501001], 103) > DATEADD(day, -30, Convert(date, GETDATE()));

Then, you can fix the data in your table. Don't store dates as strings. Store them using native types.