> On May 25, 2026, at 17:31, Chao Li <[email protected]> wrote:
>
> Hi,
>
> I just started to test “Add support for altering CHECK constraint
> enforceability”. I read the related ALTER TABLE doc first, and found it a bit
> confusing:
> ```
> ALTER CONSTRAINT
> This form alters the attributes of a constraint that was previously
> created. Currently FOREIGN KEY and CHECK constraints may be altered in this
> fashion, but see below.
> ```
>
> In the feature commit 342051d73, only “CHECK" was added:
> ```
> --- a/doc/src/sgml/ref/alter_table.sgml
> +++ b/doc/src/sgml/ref/alter_table.sgml
> @@ -578,8 +578,8 @@ WITH ( MODULUS <replaceable
> class="parameter">numeric_literal</replaceable>, REM
> <listitem>
> <para>
> This form alters the attributes of a constraint that was previously
> - created. Currently only foreign key constraints may be altered in
> - this fashion, but see below.
> + created. Currently <literal>FOREIGN KEY</literal> and
> <literal>CHECK</literal>
> + constraints may be altered in this fashion, but see below.
> </para>
> ```
>
> However, the last phrase “but see below” is quite confusing. I read the doc
> several times up and down, and finally my best guess is that “see below”
> refers to the immediately following paragraph’s sentence “Only not-null
> constraints may be altered in this fashion at present”, but the sentence does
> not say anything about enforceability.
> ```
> ALTER CONSTRAINT ... INHERIT
> ALTER CONSTRAINT ... NO INHERIT
> These forms modify an inheritable constraint so that it becomes not
> inheritable, or vice-versa. **Only not-null constraints may be altered in
> this fashion at present.** In addition to changing the inheritability status
> of the constraint, in the case where a non-inheritable constraint is being
> marked inheritable, if the table has children, an equivalent constraint will
> be added to them. If marking an inheritable constraint as non-inheritable on
> a table with children, then the corresponding constraint on children will be
> marked as no longer inherited, but not removed.
> ```
>
> As I understand it, the current behavior is:
> * Deferrability attributes can only be altered for FOREIGN KEY constraints
> * Enforceability attributes can be altered for both FOREIGN KEY and CHECK
> constraints, and CHECK support was newly added by 342051d73 for v19
>
> To remove the confusion, I updated the documentation. See the attached patch
> for details.
>
> Best regards,
> --
> Chao Li (Evan)
> HighGo Software Co., Ltd.
> https://www.highgo.com/
>
>
>
>
> <v1-0001-doc-Clarify-ALTER-CONSTRAINT-enforceability-behav.patch>
As I found a bug of the feature and proposed a fix in [1], let's merge this
thread into that one, as they are for the same feature.
[1] https://postgr.es/m/[email protected]
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
