Re: not null constraints, again

Alvaro Herrera <alvherre@alvh.no-ip.org> 于2024年8月31日周六 11:59写道：

> Hello
>
> Here I present another attempt at making not-null constraints be
> catalogued.  This is largely based on the code reverted at 9ce04b50e120,
> except that we now have a not-null constraint automatically created for
> every column of a primary key, and such constraint cannot be removed
> while the PK exists.  Thanks to this, a lot of rather ugly code is gone,
> both in pg_dump and in backend -- in particular the handling of NO
> INHERIT, which was needed for pg_dump.
>
> Noteworthy psql difference: because there are now even more not-null
> constraints than before, the \d+ display would be far too noisy if we
> just let it grow.  So here I've made it omit any constraints that
> underlie the primary key.  This should be OK since you can't do much
> with those constraints while the PK is still there.  If you drop the PK,
> the next \d+ will show those constraints.
>
> One thing that regretfully I haven't yet had time for, is paring down
> the original test code: a lot of it is verifying the old semantics,
> particularly for NO INHERIT constraints, which had grown ugly special
> cases.  It now mostly raises errors; or the tests are simply redundant.
> I'm going to remove that stuff as soon as I'm back on my normal work
> timezone.
>
> sepgsql is untested.
>
> I'm adding this to the September commitfest.
>

The attached patch adds  List *nnconstraints, which store the not-null
definition, in struct CreateStmt.
This makes me a little confused about List *constraints in struct
CreateStmt. Actually, the List constraints
store ckeck constraint, and it will be better if the comments can reflect
that. Re-naming it to List *ckconstraints
seems more reasonable. But a lot of codes that use stmt->constraints will
be changed.

Since AddRelationNewConstraints() can now add not-null column constraint,
the comments about AddRelationNewConstraints()
should tweak a little.
"All entries in newColDefaults will be processed.  Entries in
newConstraints
will be processed only if they are CONSTR_CHECK type."
Now, the type of new constraints may be not-null constraints.


If the column has already had one not-null constraint, and we add same
not-null constraint again.
Then the code will call AdjustNotNullInheritance1() in
AddRelationNewConstraints().
The comments
before entering AdjustNotNullInheritance1() in AddRelationNewConstraints()
look confusing to me.
Because constraint is not inherited.

-- 
Tender Wang