RE: table aliases save time when parsing??

From: Gillies, Garry <garry_at_weir.co.uk>
Date: Tue, 10 Jul 2001 07:15:25 -0700
Message-ID: <F001.0034556E.20010710053611@fatcity.com>

<SPAN

class=238030411-10072001>Consider
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size=2>SQL> select deptno from emp,
dept; select deptno from emp,
dept        * ERROR at line 1:
ORA-00918: column ambiguously defined
 
The
column deptno would be checked against one of the tables and would be found to
be
valid, but the checking cannot stop there. The other table must also be checked for
a
possible conflict ( which there is in this case ).
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select
d.deptno from emp e, dept d;
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Does
not just resolve the conflict, it removes the need for any checking on emp.
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Any
column which is not aliased will have to be checked against ALL tables mentioned,
so
aliasing can save quite a lot of time.
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<SPAN

class=238030411-10072001>Regards
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Garry<SPAN
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<SPAN

class=770113312-10072001> <FONT
face="Times New Roman">-----Original
Message-----From: novicedba
[mailto:novicedba_at_hotmail.com]Sent: 10 July 2001 12:11

  Hi,
    was reading
  CorrelatedSubqueries.pdf from
  oriole corp.
  In fact it's good programming
  practice to use aliases in every situation where more than one table is   referred to in a statement, since it saves time when <FONT   face="Times New Roman" size=3>parsin<FONT   face="Times New Roman" size=3>g.
   
  Can some one please explain how it

  helps?++++++++++++++++++++++++++++++++++++

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Received on Tue Jul 10 2001 - 09:15:25 CDT