| From: | jian he <jian(dot)universality(at)gmail(dot)com> |
|---|---|
| To: | Álvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | Masahiro Ikeda <ikedamsh(at)oss(dot)nttdata(dot)com>, Robert Treat <rob(at)xzilla(dot)net>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Doc: fix the rewrite condition when executing ALTER TABLE ADD COLUMN |
| Date: | 2025-03-24 01:43:36 |
| Message-ID: | CACJufxGLcbFVS8xAC9OBPn0U_2YjKOiHLdmBrtds1j=5eA5MMA@mail.gmail.com |
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| Lists: | pgsql-hackers |
hi.
https://git.postgresql.org/cgit/postgresql.git/commit/?id=11bd8318602fc2282a6201f714c15461dc2009c6
+ Adding a column with a volatile <literal>DEFAULT</literal>
+ (e.g., <function>clock_timestamp()</function>), a generated column
+ (e.g., <literal>GENERATED BY DEFAULT AS IDENTITY</literal>), a domain
+ data type with constraints will require the entire table and its
+ indexes to be rewritten, as will changing the type of an existing
+ column. As an exception, when changing the type of an existing column,
+ if the <literal>USING</literal> clause does not change the column
+ contents and the old type is either binary coercible to the new type
+ or an unconstrained domain over the new type, a table rewrite is not
+ needed.
In the current development branch,
virtual generated columns still do not support the domain.
you can not change the generation expression if it contains a check
constraint on it.
so virtual generated columns don't need rewriting.
IMHO, the committed doc description didn't mention this exception.
we need some text to cover this exception?
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