From: "Weck, Luis" <luis.weck@pismo.io>
To: "pgsql-performance@lists.postgresql.org"
	<pgsql-performance@lists.postgresql.org>
Subject: Constraints elimination during runtime
Thread-Topic: Constraints elimination during runtime
Thread-Index: AQHbrsAaMviBlb+X7USMHaFEypL3cQ==
Date: Wed, 16 Apr 2025 11:16:32 +0000
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I am not sure if this list is the most appropriate, but I figured I=92d sha=
re it here=85

If a column has a check constraint, such as CHECK (length(value) < 10) or e=
ven something like a VARCHAR(10) shouldn=92t a query like this become a no-=
op/false instantly?

  create table test_constraint (
     value varchar(10) // could be a CHECK constraint also
  );

insert into test_constraint values (=91small=92);

-- shouldn=92t this qual always evaluate to false?
select * from test_constraint where value =3D =91way too big to fit anyway=
=92;


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<html>
<head>
<meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DWindows-1=
252">
</head>
<body>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
I am not sure if this list is the most appropriate, but I figured I=92d sha=
re it here=85</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<br>
</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
If a column has a check constraint, such as CHECK (length(value) &lt; 10) o=
r even something like a VARCHAR(10) shouldn=92t a query like this become a =
no-op/false instantly?</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<br>
</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
&nbsp; create table test_constraint (
<div>&nbsp; &nbsp; &nbsp;value varchar(10) // could be a CHECK constraint a=
lso</div>
&nbsp; );<br>
</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<br>
</div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
insert into&nbsp;<span style=3D"text-decoration: none; display: inline !imp=
ortant; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">test_co=
nstraint values (=91small=92);</span></div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<span style=3D"text-decoration: none; display: inline !important; color: rg=
b(0, 0, 0); background-color: rgb(255, 255, 255);"><br>
</span></div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<span style=3D"text-decoration: none; display: inline !important; color: rg=
b(0, 0, 0); background-color: rgb(255, 255, 255);">-- shouldn=92t this qual=
 always evaluate to false?&nbsp;</span></div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<span style=3D"text-decoration: none; display: inline !important; color: rg=
b(0, 0, 0); background-color: rgb(255, 255, 255);">select * from test_const=
raint where value =3D =91way too big to fit anyway=92;&nbsp;</span></div>
<div dir=3D"ltr" style=3D"font-family: Aptos, Arial, Helvetica, sans-serif;=
 font-size: 12pt;">
<span style=3D"text-decoration: none; display: inline !important; color: rg=
b(0, 0, 0); background-color: rgb(255, 255, 255);"><br>
</span></div>
</body>
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