Solved

SQL DateTime Comparison

Posted on 2000-04-06
11
213 Views
Last Modified: 2010-04-04
I want to select records with a time stamp of (now - n*hours).  I'm using D3 and Paradox tables. Here's what I've done that doesn't work:

q is tquery
lastplay is tdatetime
n is integer

 q.Close;
 q.SQL.Clear;
 q.SQL.Add('select * from tracks where lastplay < :param');

 q.ParamByName('param').AsDateTime := now - n/24;
 q.Open;

what am i missing? it must be something simple.
0
Comment
Question by:rwv
  • 4
  • 3
  • 2
  • +2
11 Comments
 
LVL 27

Expert Comment

by:kretzschmar
ID: 2692301
? rwv,

where is the problem?
have done just a test and it works properly

sample code

//query holds : select * from time_db where dt < :param
procedure TForm1.Button1Click(Sender: TObject);
begin
  query1.Close;
  query1.ParamByName('param').AsDateTime := now - (strtoint(edit1.text)/24);
  query1.Open;
end;

do you get an errormessage?

meikl
0
 
LVL 6

Expert Comment

by:wimmeyvaert
ID: 2692311
Hi rwv,

What error do you get ?

Regards,
The Mayor
0
 
LVL 2

Expert Comment

by:Felixin
ID: 2692370
Hi, RWY and all of you


Are you sure that the conversion to hours of N/24 is OK?

Why don't you use

function EncodeTime(Hour, Min, Sec, MSec: Word): TDateTime;

calling it like this

EncodeTime (MyNumberOFHours, 0, 0, 0);

The problem is that I don't understand what you mean by "It doesn't work". Do you have any kind of error message or, simply, you don't get the result that you where expecting?

Best regards
0
 
LVL 27

Expert Comment

by:kretzschmar
ID: 2692375
felixin
n/24 is ok
meikl
0
 
LVL 9

Expert Comment

by:ITugay
ID: 2692436
listening...
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 

Author Comment

by:rwv
ID: 2692470
no error, i'm just not getting the result i expect.
my sql statement is a little more complex.  i'll look it over more closely and let you know.
0
 
LVL 9

Expert Comment

by:ITugay
ID: 2692495
rwv,
can you show us your SQL and table structures? It will easy to help you.
-----
Igor.
0
 

Author Comment

by:rwv
ID: 2692593
I've simplified my query and it still isnt working right.  

I'm using the var tn just to look at the values at a break point, they seem to be ok.

I've discovered something curious:
When set the value of the table's field (lastplay) to now() with an update query, the select query fails to exclude this record.
However, when I edit this record in a dbgrid, by only retyping a character of the date string, and then post it, the query works as expected.

Any ideas?

The only field below that really matters is lastplay which is a tDateTime.

function TfrmJBox.TrackQuery(cdid : integer) : boolean;
var ok : boolean;
    qwhere : string;
    tn : tdatetime;
begin
  ok := true;

    qwhere := 'where (cdid ='+inttostr(cdid)+') and ((lastplay < :dtlastplay) or (lastplay is null)) ';

  try
    if qTracks.State <> dsInactive then
      qTracks.Close;
    qTracks.SQL.Clear;
    qTracks.SQL.Add('select '+
                   'trackno, tracklen, title, votes, points, plays, lastplay, id, artist '+
                   'from "'+gDataDir+'\tracks.db" '+
                   qwhere+
                   'order by trackno');
    tn := now;
    qTracks.ParamByName('dtlastplay').AsDateTime := tn - gMinReplayTime/24;
    qTracks.Open;
  except
    ok := false;
  end;
  TrackQuery := ok;
end;
0
 
LVL 9

Accepted Solution

by:
ITugay earned 200 total points
ID: 2692625
Still thinking...
but one crazy idea, is it possible you have different datetime format while making update by update query(dd/mm/yy and mm/dd/yy)?
----
Igor.
0
 

Author Comment

by:rwv
ID: 2693683
Igor,
I didnt change datetime format, but you did lead me to the solution:
I was using
  ' set lastplay = "'+DateTimeToStr(now)+'"'
changed it to
  ' set lastplay = :paramNow'
then AddParamByName('paramNow').AsDateTime

However, I dont understand why this makes a difference.  Aren't Tdatetime types just numbers once they are stored?

Thanks all for your help to everyone.

Bobby Valentine
0
 

Author Comment

by:rwv
ID: 2693691
correction
' set lastplay = :paramNow'
ParamByName('paramNow').AsDateTime := now;


 
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
Hello everybody This Article will show you how to validate number with TEdit control, What's the TEdit control? TEdit is a standard Windows edit control on a form, it allows to user to write, read and copy/paste single line of text. Usua…
This Micro Tutorial will give you a basic overview how to record your screen with Microsoft Expression Encoder. This program is still free and open for the public to download. This will be demonstrated using Microsoft Expression Encoder 4.
Sending a Secure fax is easy with eFax Corporate (http://www.enterprise.efax.com). First, just open a new email message. In the To field, type your recipient's fax number @efaxsend.com. You can even send a secure international fax — just include t…

863 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

19 Experts available now in Live!

Get 1:1 Help Now