LIMIT and JOINS

<div class="Section1"><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">Hi,</span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB" style="font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">I have a question on implementation of the LIMIT SQL
clause.</span></font><pclass="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Using the LIMIT clause, I want to reduce the computation time for a
query.</span></font><pclass="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">When I try to limit the result of a joined table, however, the join
willbe computed first (which takes very long).</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><span class="GramE"><font
face="Arial"size="2"><span lang="EN-GB"
style="font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Lets</span></font></span><fontface="Arial"
size="2"><spanlang="EN-GB" style="font-size:10.0pt;font-family:Arial; 
mso-ansi-language:EN-GB"> suppose the following example:</span></font><p class="MsoNormal"><font face="Arial"
size="2"><spanlang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><span class="GramE"><font
face="Arial"size="2"><span lang="EN-GB"
style="font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB">select</span></font></span><fontface="Arial"
size="2"><spanlang="EN-GB" style="font-size:10.0pt;font-family:Arial; 
mso-ansi-language:EN-GB"> * from T1 join T2 on T1.id = T2.id LIMIT 1</span></font><p class="MsoNormal"><font
face="Arial"size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Conceptually, it should be possible to fetch one row from T1 and T2,
i.e.to propagate the LIMIT clause.</span></font><p class="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB"
style="font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">I was wondering what the exact requirements are to propagate the
LIMITclause.</span></font><p class="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Do I need a foreign key relation between T1 and T2?</span></font><p
class="MsoNormal"><fontface="Arial" size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Do I need to use a full outer join in order to propagate the LIMIT
clause?</span></font><pclass="MsoNormal"><font face="Arial" size="2"><span lang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span
lang="EN-GB"style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB">Thanks</span></font><p class="MsoNormal"><font face="Arial"
size="2"><spanlang="EN-GB" style="font-size: 
10.0pt;font-family:Arial;mso-ansi-language:EN-GB"> </span></font><p class="MsoNormal"
style="mso-layout-grid-align:none"><fontface="Arial" size="2"><span lang="EN-GB"
style="font-size:10.0pt;font-family:Arial;mso-ansi-language:EN-GB;mso-bidi-font-weight:bold;mso-no-proof:yes">Gregor
Zeitlinger</span></font><fontface="Arial" size="2"><span lang="EN-GB"
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