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Home -> Community -> Mailing Lists -> Oracle-L -> Re: SQL Join or Subquery
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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-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Gary Chambers INET: gc22_at_lucent.com 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). =================================================================== De informatie verzonden in dit e-mailbericht is vertrouwelijk en is uitsluitend bestemd voor de geadresseerde. Openbaarmaking, vermenigvuldiging, verspreiding en/of verstrekking van deze informatie aan derden is, behoudens voorafgaande schriftelijke toestemming van Ernst & Young, niet toegestaan. Ernst & Young staat niet in voor de juiste en volledige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor tijdige ontvangst daarvan. Ernst & Young kan niet garanderen dat een verzonden e-mailbericht vrij is van virussen, noch dat e-mailberichten worden overgebracht zonder inbreuk of tussenkomst van onbevoegde derden. Indien bovenstaand e-mailbericht niet aan u is gericht, verzoeken wij u vriendelijk doch dringend het e-mailbericht te retourneren aan de verzender en het origineel en eventuele kopieën te verwijderen en te vernietigen. Ernst & Young hanteert bij de uitoefening van haar werkzaamheden algemene voorwaarden, waarin een beperking van aansprakelijkheid is opgenomen. De algemene voorwaarden worden u op verzoek kosteloos toegezonden. ===================================================================== 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 - 03:38:19 CDT
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