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Re: SQL Join or Subquery

From: Jack van Zanen <nlzanen1_at_EY.NL>
Date: Thu, 18 Jul 2002 02:33:17 -0800
Message-ID: <F001.0049B11A.20020718023317@fatcity.com> 





Or with the sensor name included



select  t1.sensor_id,s.naam,t1.temp_c


from temperature t1, sensor s


where t1.timestamp = (select max(t2.timestamp)

                      from temperature t2
                      where t1.sensor_id=t2.sensor_id)


and s.sensor_id=t1.sensor_id



11:30:15 29-CC1-JACK> select * from temperature
11:30:25   2  /



 SENSOR_ID     TEMP_C TIMESTAMP



---------- ---------- -----------------


         1         15 18-jul-2002 09:25
         2         16 18-jul-2002 09:25
         1         11 18-jul-2002 09:25
         2         18 18-jul-2002 09:25
         3         17 18-jul-2002 09:25
         1         15 18-jul-2002 09:25
         2         15 18-jul-2002 09:25
         3         15 18-jul-2002 09:25
         1         11 18-jul-2002 09:25
         2         12 18-jul-2002 09:25
         3        110 18-jul-2002 09:25
         2         12 18-jul-2002 09:30
         3        110 18-jul-2002 09:30
         1         11 18-jul-2002 09:30





14 rows selected.



11:30:26 29-CC1-JACK> select * from sensor
11:30:53   2  /



 SENSOR_ID NAAM



---------- ------------------------------


         1 sensor1
         2 sensor2
         3 sensor3





11:30:54 29-CC1-JACK> @xx


 SENSOR_ID NAAM                               TEMP_C


---------- ------------------------------ ----------

         1 sensor1                                11
         2 sensor2                                12
         3 sensor3                               110





11:31:02 29-CC1-JACK>






                                                                                                                                       
                      "Jack van Zanen"                                                                                                 
                      <nlzanen1_at_ey.nl>         To:       Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                   
                      Sent by:                 cc:       (bcc: Jack van Zanen/nlzanen1/External/MEY/NL)                                
                      root_at_fatcity.com         Subject:  Re: SQL Join or Subquery                                                      
                                                                                                                                       
                                                                                                                                       
                      18-07-2002 10:38                                                                                                 
                      Please respond to                                                                                                
                      ORACLE-L                                                                                                         
                                                                                                                                       
                                                                                                                                       







Hi




Try:



select  t1.sensor_id,t1.temp_c


from temperature t1


where t1.timestamp = (select max(t2.timestamp)

                                        from temperature t2
                    where t1.sensor_id=t2.sensor_id)






Jack




                      Gary Chambers

                      <gc22_at_lucent.com>        To:       Multiple
recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
                      Sent by:                 cc:       (bcc: Jack van
Zanen/nlzanen1/External/MEY/NL)
                      root_at_fatcity.com         Subject:  SQL Join or


Subquery



                      17-07-2002 23:54

                      Please respond to

                      ORACLE-L










All...



I have a question about a query over which I've been racking my brain
for weeks, and I can't find a reference to adequately assist me.



Given a table of temperature sensors, and a table of readings from those
sensors, how might I grab the max (hence latest or current) temperature
reading for each sensor?  The relevant fields in the tables are
timestamp and temp_c (temperature table), and sensorid (both temperature
and sensor tables).



I'm fairly certain that I'm overlooking something very elementary, and I
feel it should be simple and straightforward, but I think I'm being
stymied by the use of aggregate functions in my query.  I can provide
examples of my failed attempts, if you'd like.  Thanks in advance for
any assistance you can provide.



Gary Chambers


//-------------------------------------
// Lucent Technologies GIO/Unix
// 4 Robbins Road, Westford, MA 01886
// 978-399-0481 / 888-480-6924 (Pager)




// Nothing fancy and nothing Microsoft

//-------------------------------------






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Author: Gary Chambers


  INET: gc22_at_lucent.com


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Author: Jack van Zanen


  INET: nlzanen1_at_EY.NL


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addressed. You should not copy, disclose or distribute this communication
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the proper and complete transmission of the information contained in this
communication nor for any delay in its receipt. Ernst & Young does not
guarantee that the integrity of this communication has been maintained nor
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If you are not the intended recipient of this communication please return
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Please see the official ORACLE-L FAQ: http://www.orafaq.com


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Author: Jack van Zanen


  INET: nlzanen1_at_EY.NL


Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists


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Received on Thu Jul 18 2002 - 05:33:17 CDT












Original text of this message













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