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Re: SQL Join or Subquery

From: Jack van Zanen <nlzanen1_at_EY.NL>
Date: Thu, 18 Jul 2002 00:38:19 -0800
Message-ID: <F001.0049B045.20020718003819@fatcity.com>


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

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Author: Gary Chambers
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-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Jack van Zanen
  INET: nlzanen1_at_EY.NL

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Received on Thu Jul 18 2002 - 03:38:19 CDT

Original text of this message

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