From: ma lz <ma100@hotmail.com>
To: "pgsql-general@postgresql.org" <pgsql-general@postgresql.org>
Subject: Why not do distinct before SetOp
Thread-Topic: Why not do distinct before SetOp
Thread-Index: AQHbLp7dvNXHmMJ32UeiUjfJ44a5RA==
Date: Mon, 4 Nov 2024 09:52:12 +0000
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<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Dgb2312">
<style type=3D"text/css" style=3D"display:none;"> P {margin-top:0;margin-bo=
ttom:0;} </style>
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<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
some sql like ' select a from t1 intersect select a from t1 '</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
if t1 has large number rows but has few distinct rows</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
select distinct a from t1 intersect select distinct a&nbsp;from t1;&nbsp; &=
nbsp; =A1=AA this is faster than origin sql</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class=3D"elementToProof" style=3D"font-family: Calibri, Helvetica, san=
s-serif; font-size: 12pt; color: rgb(0, 0, 0);">
can postgres do this optimize during plan-queries?</div>
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