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Re: Basic Database Question

From: Jack van Zanen <nlzanen1_at_EY.NL>
Date: Wed, 15 May 2002 07:13:28 -0800
Message-ID: <F001.0046122E.20020515071328@fatcity.com>

Hi,

Outer joins can still return rows when no match exists(or empty)

Jack

                                                                                                                                       
                      "Gavin D'Mello"                                                                                                  
                      <gavin_d_at_tis.co.i        To:       Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                   
                      n>                       cc:       (bcc: Jack van Zanen/nlzanen1/External/MEY/NL)                                
                      Sent by:                 Subject:  Basic Database Question                                                       
                      root_at_fatcity.com                                                                                                 
                                                                                                                                       
                                                                                                                                       
                      15-05-2002 16:03                                                                                                 
                      Please respond to                                                                                                
                      ORACLE-L                                                                                                         
                                                                                                                                       
                                                                                                                                       



Hi I'm just about to ask a really trivial question which has never struck me before.

If i write a simple select like

select c.contentid from content c,
persusercontentassoc p,
teachercontentassoc t
where
t.contentid = c.contentid OR
p.contentid = c.contentid;

and if the table persusercontentassoc is empty no rows are returned. However, if i populate this table i get meaningful data. So what i'm asking is if any one table in a select contains no data will the select always return no rows ?

Thanks,

Gavin



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Author: Jack van Zanen
  INET: nlzanen1_at_EY.NL

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