Re: Re: starting to review the Extend NOT NULL representation to pg_constraint patch

Excerpts from Robert Haas's message of mié jun 29 13:07:25 -0400 2011:
> On Wed, Jun 29, 2011 at 12:51 PM, Alvaro Herrera
> <alvherre(at)commandprompt(dot)com> wrote:
> > Excerpts from Robert Haas's message of lun jun 27 10:35:59 -0400 2011:

> > Interesting.  This whole thing requires quite a bit of rejiggering in
> > the initial transformation phase, I think, but yeah, I see the points
> > here and I will see to them.  Does this mean that "NOT NULL PRIMARY KEY"
> > now behaves differently?  I think it does , because if you drop the PK
> > then the field needs to continue being not null.
>
> Yeah, I think an implicit not-null because you made it a primary key
> is now different from one that you write out.

Actually, it wasn't that hard, but I'm not really sure I like the
resulting code:

/*
* We want to inherit NOT NULL constraints, but not primary keys.
* Since attnotnull flags in pg_attribute stores both, we want to keep only
* the attnotnull flag from those columns that have it from NOT NULL
* constraints. To do this, we create a copy of the table's descriptor
* and scribble on it by resetting all the attnotnull bits to false, and
* the setting them true for columns that appear in a NOT NULL constraint.
*
* Note: we cannot use CreateTupleDescCopy here, because it'd lose
* the atthasdef bits, as well as constraints.
*/
tupleDesc = CreateTupleDescCopyConstr(RelationGetDescr(relation));
constr = tupleDesc->constr;
parent_nns = GetRelationNotNullConstraints(relation);

for (parent_attno = 1; parent_attno <= tupleDesc->natts;
parent_attno++)
tupleDesc->attrs[parent_attno - 1]->attnotnull = false;

foreach (cell, parent_nns)
{
NotNullConstraint *constr = lfirst(cell);

tupleDesc->attrs[constr->attnum - 1]->attnotnull = true;
}

Here's the simple example (sorry for the spanish):

alvherre=# create table foo (a int primary key, b int not null);
NOTICE: CREATE TABLE / PRIMARY KEY creará el índice implícito «foo_pkey» para la tabla «foo»
CREATE TABLE
alvherre=# create table bar () inherits (foo);
CREATE TABLE

alvherre=# \d foo
Tabla «public.foo»
Columna | Tipo | Modificadores
---------+---------+---------------
a | integer | not null
b | integer | not null
Índices:
"foo_pkey" PRIMARY KEY, btree (a)
Número de tablas hijas: 1 (Use \d+ para listarlas.)

alvherre=# \d bar
Tabla «public.bar»
Columna | Tipo | Modificadores
---------+---------+---------------
a | integer |
b | integer | not null
Hereda: foo

alvherre=# create table baz (a int not null primary key);
NOTICE: CREATE TABLE / PRIMARY KEY creará el índice implícito «baz_pkey» para la tabla «baz»
CREATE TABLE
alvherre=# create table qux () inherits (baz);
CREATE TABLE
alvherre=# \d baz
Tabla «public.baz»
Columna | Tipo | Modificadores
---------+---------+---------------
a | integer | not null
Índices:
"baz_pkey" PRIMARY KEY, btree (a)
Número de tablas hijas: 1 (Use \d+ para listarlas.)

alvherre=# \d qux
Tabla «public.qux»
Columna | Tipo | Modificadores
---------+---------+---------------
a | integer | not null
Hereda: baz

--
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
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