asked on

Select Top 5 from Table

How do you select the Top n records in a query or Stored Procedure.

my current Stored Procedure is as follows:

create Procedure nspTopDTMAchines (TopRecords Integer)
Returns (MachineName Varchar(10), MachDownTime Integer)
as
begin
for
      Select dtd.MachineName, Sum(dtd.DownTime)

      FROM nvDownTimeDetails dtd

      GROUP BY dtd.MachineName

      ORDER BY 2 DESC

      Into :MachineName, :MachDownTime

      do suspend;
end;

I need to use the parameter TopRecords to determine how many Records to return.

Thanks,
matchbx

matchbx27

ASKER

Here's the Solution:

create Procedure nspTopDTMAchines (TopRecords Integer)
Returns (MachineName Varchar(10), MachDownTime Integer)
as
DECLARE VARIABLE iCount INTEGER;
begin

iCount = 0;

for
Select dtd.MachineName, Sum(dtd.DownTime)

FROM nvDownTimeDetails dtd

GROUP BY dtd.MachineName

ORDER BY 2 DESC

Into :MachineName, :MachDownTime

      DO
      BEGIN
           iCount = iCount + 1;
     IF (iCount <= :TopRecords) THEN
       SUSPEND;
     ELSE
      EXIT;
      END

suspend;
end;

matchbx27

ASKER

Question Answered

vowca

Yaffil and Firebird can use the following pattern:
SELECT [FIRST(10)] [SKIP(2)] <rows> FROM ....
IB 7.x (and maybe 6.5) has a similar compatibility bat looks something alike SELECT .......... ROWS 3 TO 13

It is now discussed if FB 2.x will have SQL standard ROWS option for select (IB's one is not, nor is FIRST/SKIP)

Also remember that those boundaries are applied after select is started fetching - hence it will not change its plan, it will not speed up the very select (but may speed up network transmition just because there will be less data to transfer)

vowca

PS: if q. is answered - plz close the issue.
https://www.experts-exchange.com/questions/20703934/Correct-DELETE-syntax-in-Delphi-using-ADO.html
Currently You answer is marked as UNanswered.

matchbx27

ASKER

The comments provided by vowca will not work for Interbase 5.5, but I guess thats my fault since I did not specify a database verison. If you are using Interbase 5.5 you have to use a Stored Procedure. Please see my comment above.

vowca

Points are given back.

as: upgrade at least for 5.6! 5.x is known for its bugs, even i stumbled acrross some of them.

Then give a try to Yaffil. Amount of bugs found in IB6.0 and prior is just shoking.
Indeed, last reason for merging Firebird and Yaffil was that their teams together hunted for ForeignKey corruption bug, that was present at least in IB 4.0
And Yaffil has special measures to be compatible with 5.x generation.

Now one more tweak - use generator - it may work bad for concurrent transactions but sometimes it helps.

1st i set generator to some value:
select gen_id(G_RUL, -gen_id(g_rul, 0) /* drom to zero */ + /* new value*/ 10) from rdb$database
( SET GENERATOR might be taken for metadata change and force backup/restore)

Now:
select * from LOG
where /* some conditions AND */ gen_id(G_RUL, -1) >= 0

PS: to be true, this hack filters ouptput, but IB still tries on record after another, so, say, for 1000000 rows table it will be rather long anyway.
The records would not be sent to client, but will be tried by server kernel.

One more rook is that i do not know, what is executed first - order by or checking for where

ASKER CERTIFIED SOLUTION

PashaMod

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Hornwood

Firebird SQL :-

select first 10 * from Table