| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
 |
 | |||
| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
|
| |||
Home -> Community -> Mailing Lists -> Oracle-L -> Re[2]: table aliases save time when parsing??
Igor,
Square hit as I remember it. I've read a couple of items from oriole corp and while I have never found anything they've written to be wrong, they have been less than completely clear on the why's and wherefores as in this case.
Dick Goulet
____________________Reply Separator____________________ Author: "Igor Neyman" <ineyman_at_perceptron.com> Date: 7/10/2001 5:26 AM
Well, it's not aliases themselves, but the practice of using aliases as prefixes, when referring to columns:
SELECT t1.col1, t1.col2, t2.col1
FROM table1 t1, table2 t2
WHERE t1.col2 = t2.col2
that's what saves time when parsing: this way you tell the parser which table column list to look for, otherwise (when no prefixes used) it has to search through all tables column lists for particular column definition (and also to make sure, that this column name is unique in all column lists - if not you'll be getting an error, if not using prefixes).
But, you can get the same result (save time on parsing), when using table names as prefixes:
SELECT table1.col1, table1.col2, table2.col1
FROM table1, table2
WHERE table1.col2 = table2.col2
It's just that aliases are usually short (while table names could be long), and it's easier to read the code.
List, please correct me, if I'm wrong.
Igor Neyman, OCP DBA
Perceptron, Inc.
(734)414-4627
ineyman_at_perceptron.com
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
parsing.
Can some one please explain how it helps?
coz
I am a
novice
Oracle Certifiable DBBS
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 5.50.4522.1800" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2>Well, it's not aliases themselves, but the practice of using
aliases as prefixes, when referring to columns:</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>SELECT t1.col1, t1.col2, t2.col1</FONT></DIV>
<DIV><FONT size=2>FROM table1 t1, table2 t2</FONT></DIV>
<DIV><FONT size=2>WHERE t1.col2 = t2.col2</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>that's what saves time when parsing: this way you tell the
parser which table column list to look for, otherwise (when no
prefixes used) it has to search through all tables column lists for
particular column definition (and also to make sure, that this column name
is unique in all column lists - if not you'll be getting an error, if not using
prefixes).</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>But, you can get the same result (save time on parsing), when
using table names as prefixes:</FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>
<DIV><FONT size=2>SELECT table1.col1, table1.col2, table2.col1</FONT></DIV>
<DIV><FONT size=2>FROM table1, table2</FONT></DIV>
<DIV><FONT size=2>WHERE table1.col2 = table2.col2</FONT></DIV>
<DIV> </DIV>
<DIV>It's just that aliases are usually short (while table names could be long),
and it's easier to read the code.</DIV>
<DIV> </DIV>
<DIV>List, please correct me, if I'm wrong.</DIV></FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV>Igor Neyman, OCP DBA<BR>Perceptron, Inc.<BR>(734)414-4627<BR><A
href="mailto:ineyman_at_perceptron.com">ineyman_at_perceptron.com</A><BR>
<BR></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT:
#000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=novicedba_at_hotmail.com
href="mailto:novicedba_at_hotmail.com">novicedba</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=ORACLE-L_at_fatcity.com
href="mailto:ORACLE-L_at_fatcity.com">Multiple recipients of list ORACLE-L</A>
</DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, July 10, 2001 7:10 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> table aliases save time whenparsing??</DIV>
<DIV><BR></DIV> <DIV><FONT face=Arial size=2>Hi,</FONT></DIV> <DIV><FONT face=Arial size=2> was reading <STRONG>CorrelatedSubqueries.pdf </STRONG></FONT><FONT face=Arial size=2>fromoriole corp.</FONT></DIV>
practice to use aliases in every situation where more than one table is
referred to in a statement, since it saves time when </STRONG></FONT><I><FONT
face="Times New Roman" size=3><STRONG>parsin</STRONG></I></FONT><FONT
face="Times New Roman" size=3><STRONG>g.</STRONG></FONT></DIV>
<DIV><FONT face="Times New Roman" size=3></FONT> </DIV>
<DIV><FONT face="Times New Roman" size=3>Can some one please explain how it
helps?</FONT></DIV>
<DIV><FONT face="Times New Roman" size=3> </DIV></FONT>
<DIV><FONT face=Arial size=2>coz<BR>I am a<BR>novice<BR>Oracle Certifiable
DBBS</FONT></DIV></BLOCKQUOTE></BODY></HTML>
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: dgoulet_at_vicr.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).Received on Tue Jul 10 2001 - 08:26:43 CDT
 |
 |