From: "Weck, Luis" <luis.weck@pismo.io>
To: Marcelo Fernandes <marcefern7@gmail.com>,
	"pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Subject: Re: Increasing a NUMERIC column precision doesn't cause a table
 rewrite. Why?
Thread-Topic: Increasing a NUMERIC column precision doesn't cause a table
 rewrite. Why?
Thread-Index: AQHcTJtWqRhwKOeFB06xKsQ85qqgkbTg0icO
Date: Mon, 3 Nov 2025 11:35:39 +0000
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My understanding is that Postgres can guarantee that all the values in the =
table will fit the new precision without having to check. If you change the=
 scale, it might be the case that some values won=92t fit anymore, and Post=
gres must return an error. Numeric by itself is a variable length type, lik=
e TEXT (in a sense). That=92s why we can modify its size without requiring =
a table rewrite at all!

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<span style=3D"font-family: Aptos; font-size: 16px; color: rgb(0, 0, 0);">M=
y understanding is that
</span><span style=3D"font-family: Aptos; font-size: 16px; color: rgb(0, 0,=
 0); background-color: rgb(255, 255, 255);">Postgres</span><span style=3D"f=
ont-family: Aptos; font-size: 16px; color: rgb(0, 0, 0);">&nbsp;can guarant=
ee that all the values in the table will
 fit the new precision without having to check. If&nbsp;you change the scal=
e, it might be the&nbsp;case that some values won=92t fit anymore, and Post=
gres&nbsp;must return an error. Numeric by itself is a variable length type=
, like TEXT (in a sense). That=92s why we can modify
 its size without requiring a table rewrite at all!</span>
<div id=3D"mail-editor-reference-message-container" dir=3D"ltr" style=3D"co=
lor: inherit; background-color: inherit;">
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