Question

Help in creating a query....

Asked by: imarshad

I need to fetch data from two tables(Vehicles, VData) in my database using the following criterion.
Vehicles table has fields (UnitID, vNo, vName) UnitID is Primary key and is unique for each record.
VData table has fields (UnitID, TimeDate, value1, value2) There are multiple records with same UnitID in this table.

Now I want to select the following
Each Unique UnitID in VData that is also present in Vehicles table and also its last record(Latest TimeDate value) from VData.

Part I of this query is easy i.e "Each Unique UnitID in VData that is also present in Vehicles table"

This can be simply done by using the following query
Select Vehicles.UnitID, Vehicles.vNo, Vehicles.vName from Vehicles where Vehicles.UnitID IN ( Select Distinct UnitID from VData)

But I am stuck as how to fetch the latest record for each UnitID in VData table.


Backend database Oracle 9i
Frontend VB6 and ADO

Sample Data and expected results......
Vehicles Table
UnitID     vNo       vName
 1001      a1         xyz
 1002      a2         xyz
 1003      a3         xyz 
 1004      a4         xyz  
 1005      a5         xyz
 
VData Table
 
UnitID        TimeDate              value1    value2
 1001     2009/04/22 10:23           (Irrelevant)
 1001     2009/04/22 10:20           (Irrelevant)
 1003     2009/04/22 11:23           (Irrelevant)
 1003     2009/04/22 12:29           (Irrelevant)
 1004     2009/04/22 11:50           (Irrelevant)
 1004     2009/04/22 10:14           (Irrelevant)
 1004     2009/04/22 06:59           (Irrelevant)
 1004     2009/04/20 02:23           (Irrelevant)
 1006     2009/04/22 12:403          (Irrelevant)
 
Expected results after running the query.....
 
1001      a1         xyz      2009/04/22 10:23   value1    value2
1003      a3         xyz      2009/04/22 12:29   value1    value2
1004      a4         xyz      2009/04/22 11:50   value1    value2

                                  
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Asked On
2009-04-22 at 21:33:26ID24347805
Topics

Oracle Database

,

Microsoft Access Database

,

Oracle 9.x

Participating Experts
4
Points
500
Comments
13

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Answers

 

by: ivostoykovPosted on 2009-04-22 at 23:41:26ID: 24212261

try following

Select Vehicles.UnitID, Vehicles.vNo, Vehicles.vName from Vehicles where Vehicles.UnitID IN ( Select UnitID from VData where TimeDate in (Select max(TimeDate) from VData group by UnitID))

                                              
1:

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by: ivostoykovPosted on 2009-04-22 at 23:43:43ID: 24212272

or variant

Select Vehicles.UnitID, Vehicles.vNo, Vehicles.vName from Vehicles where Vehicles.UnitID exists ( Select UnitID, max(TimeDate) from VData where Vehicles.UnitID = VData.UnitID group by VData.UnitID)

                                              
1:

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by: praveencpkPosted on 2009-04-23 at 00:27:25ID: 24212474

select v.unitid,v.vno,v.vname,max(vd.timedate) Timedate,vd.value1 from vehicles v,vdata vd where
v.unitid=vd.unitid
group by v.unitid,v.vno,v.vname,vd.value1

 

by: nav_kum_vPosted on 2009-04-23 at 01:04:28ID: 24212700

You can try the below :

select A.*, B.timedate, B.value1 , B.value2
from
(select unitid, vno , vname from vehicles ) A,
( select temp1.unitid unitid,
temp1.timedate timedate,
temp1.value1 value1, temp1.value2 value2
from
( select vd.unitid vd_ui, max(vd.timedate) vd_td
from vdata vd
group by vd.unitid  ) x , vdata temp1
where temp1.unitid = x.vd_ui
and temp1.timedate = x.vd_td
) B
where a.unitid = b.unitid;

 

by: imarshadPosted on 2009-04-24 at 00:35:47ID: 24222566

The query supplied by nav_kum_v works perfectly.....
ivostoykov,
How can I get the VData.TimeDate, VData.value1, VData.valu2 in both of your queries?
I will also try other suggestions as well...

 

by: awking00Posted on 2009-04-24 at 07:19:23ID: 24225482

The attached should work for you.

  • query.txt
    • 297 bytes

    Query to get latest timedate records.

 

by: imarshadPosted on 2009-04-27 at 00:53:00ID: 24239556

nav_kum_v,
In fact the query you have supplied doesnot work perfectly.... When there is a case where a UnitID has more then one record for the maximum timeDate then it returns multiple records. What I mean is explained in the Code view below....

awking00,
Your query performs perfectly but it's only drawback is that it is slow as compared to the one supplied by nav_kum_v.

VData Table
 
UnitID        TimeDate              value1    value2
 1001     2009/04/22 10:23           (Irrelevant)
 1001     2009/04/22 10:20           (Irrelevant)
 1003     2009/04/22 11:23           (Irrelevant)
 1003     2009/04/22 12:29           (Irrelevant)
 
For such a case the query runs perfectly.... But lets say I have the following records ( 1001 has two records with same Maximum Timedate then the query returns the UnitID 1001 twice). I think it can be solved by inserting a rownum=1 somewhere but I am unable to find where???
 
VData Table
 
UnitID        TimeDate              value1    value2
 1001     2009/04/22 10:23           (Irrelevant)
 1001     2009/04/22 10:23           (Irrelevant)
 1003     2009/04/22 11:23           (Irrelevant)
 1003     2009/04/22 12:29           (Irrelevant)
                                              
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by: nav_kum_vPosted on 2009-04-27 at 01:14:36ID: 24239662

i gave you that query because your initial data did not show me the duplicates.. now that you have told that, i can come up with a modified one shortly.

 

by: imarshadPosted on 2009-04-27 at 01:15:59ID: 24239671

That will be so nice of you....

 

by: nav_kum_vPosted on 2009-04-27 at 01:33:07ID: 24239757

this is one way of doing it.... not sure about the performance.. give it a try :

select unitid, vno, vname, timedate, value1, value2
from (
select A.*, B.timedate, B.value1 , B.value2 , row_number() over ( partition by a.unitid order by timedate desc ) xx
from
(select unitid, vno , vname from vehicles ) A,
( select temp1.unitid unitid,
temp1.timedate timedate,
temp1.value1 value1, temp1.value2 value2
from
( select vd.unitid vd_ui, max(vd.timedate) vd_td
from vdata vd
group by vd.unitid  ) x , vdata temp1
where temp1.unitid = x.vd_ui
and temp1.timedate = x.vd_td
) B
where a.unitid = b.unitid
)
where xx = 1 ;

 

by: nav_kum_vPosted on 2009-04-27 at 01:44:45ID: 24239809

Here is the another version....again not sure about the performance.. give this as well a try :

select a.*,
( select value1 from vdata xx where xx.unitid=a.unitid and xx.timedate = a.timedate and rownum = 1 ) value1,
( select value2 from vdata xx where xx.unitid=a.unitid and xx.timedate = a.timedate and rownum = 1 ) value2
from (  
select v.* , ( select max(timedate) from vdata vd where vd.unitid = v.unitid ) timedate
from vehicles v
where exists ( select 1 from vdata vv where vv.unitid = v.unitid )  
) a ;

 

by: nav_kum_vPosted on 2009-04-27 at 01:45:17ID: 24239810

i have tested both the queries and the results are as expected by you even with the duplicate data... BUT not sure about the performance.

 

by: imarshadPosted on 2009-04-27 at 01:54:09ID: 24239848

Thanks this one works greatly and is quite quick too.... Although it uses the same technique provided by awking000
i.e
row_number() over ( partition by a.unitid order by timedate desc ) xx

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