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
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