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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)

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Author: Gary Chambers
  INET: gc22_at_lucent.com

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Please see the official ORACLE-L FAQ: http://www.orafaq.com
--

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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The information contained in this communication is confidential and is intended solely for the use of the individual or entity to whom it is addressed. You should not copy, disclose or distribute this communication without the authority of Ernst & Young. Ernst & Young is neither liable for 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 that the communication is free of viruses, interceptions or interference.

If you are not the intended recipient of this communication please return the communication to the sender and delete and destroy all copies.

In carrying out its engagements, Ernst & Young applies general terms and conditions, which contain a clause that limits its liability. A copy of these terms and conditions is available on request free of charge.


--

Please see the official ORACLE-L FAQ: http://www.orafaq.com
--

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

--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). Received on Thu Jul 18 2002 - 05:33:17 CDT

Original text of this message

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