Add pg_constraint rows for not-null constraints

We now create contype='n' pg_constraint rows for not-null constraints on
user tables.  Only one such constraint is allowed for a column.

We propagate these constraints to other tables during operations such as
adding inheritance relationships, creating and attaching partitions and
creating tables LIKE other tables.  These related constraints mostly
follow the well-known rules of conislocal and coninhcount that we have
for CHECK constraints, with some adaptations: for example, as opposed to
CHECK constraints, we don't match not-null ones by name when descending
a hierarchy to alter or remove it, instead matching by the name of the
column that they apply to.  This means we don't require the constraint
names to be identical across a hierarchy.

The inheritance status of these constraints can be controlled: now we
can be sure that if a parent table has one, then all children will have
it as well.  They can optionally be marked NO INHERIT, and then children
are free not to have one.  (There's currently no support for altering a
NO INHERIT constraint into inheriting down the hierarchy, but that's a
desirable future feature.)

This also opens the door for having these constraints be marked NOT
VALID, as well as allowing UNIQUE+NOT NULL to be used for functional
dependency determination, as envisioned by commit e49ae8d3bc.  It's
likely possible to allow DEFERRABLE constraints as followup work, as
well.

psql shows these constraints in \d+, though we may want to reconsider if
this turns out to be too noisy.  Earlier versions of this patch hid
constraints that were on the same columns of the primary key, but I'm
not sure that that's very useful.  If clutter is a problem, we might be
better off inventing a new \d++ command and not showing the constraints
in \d+.

For now, we omit these constraints on system catalog columns, because
they're unlikely to achieve anything.

The main difference to the previous attempt at this (b0e96f3119) is
that we now require that such a constraint always exists when a primary
key is in the column; we didn't require this previously which had a
number of unpalatable consequences.  With this requirement, the code is
easier to reason about.  For example:

- We no longer have "throwaway constraints" during pg_dump.  We needed
  those for the case where a table had a PK without a not-null
  underneath, to prevent a slow scan of the data during restore of the
  PK creation, which was particularly problematic for pg_upgrade.

- We no longer have to cope with attnotnull being set spuriously in
  case a primary key is dropped indirectly (e.g., via DROP COLUMN).

Some bits of code in this patch were authored by Jian He.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Author: Bernd Helmle <mailings@oopsware.de>
Reviewed-by: 何建 (jian he) <jian.universality@gmail.com>
Reviewed-by: 王刚 (Tender Wang) <tndrwang@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Discussion: https://postgr.es/m/202408310358.sdhumtyuy2ht@alvherre.pgsql

doc/src/sgml/ref/alter_foreign_table.sgml

@@ -173,7 +173,8 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceab
      <para>
       This form adds a new constraint to a foreign table, using the same
       syntax as <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.
-      Currently only <literal>CHECK</literal> constraints are supported.
+      Currently only <literal>CHECK</literal> and <literal>NOT NULL</literal>
+      constraints are supported.
      </para>
 
      <para>
@@ -182,7 +183,8 @@ ALTER FOREIGN TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceab
       declares that some new condition should be assumed to hold for all rows
       in the foreign table.  (See the discussion
       in <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.)
-      If the constraint is marked <literal>NOT VALID</literal>, then it isn't
+      If the constraint is marked <literal>NOT VALID</literal> (allowed only for
+      the <literal>CHECK</literal> case), then it isn't
       assumed to hold, but is only recorded for possible future use.
      </para>
     </listitem>

doc/src/sgml/ref/alter_table.sgml

@@ -98,7 +98,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 <phrase>and <replaceable class="parameter">column_constraint</replaceable> is:</phrase>
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
-{ NOT NULL |
+{ NOT NULL [ NO INHERIT ] |
   NULL |
   CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
   DEFAULT <replaceable>default_expr</replaceable> |
@@ -114,6 +114,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
 { CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
+  NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
   UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
   EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
@@ -849,19 +850,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       table.  Subsequently, queries against the parent will include records
       of the target table.  To be added as a child, the target table must
       already contain all the same columns as the parent (it could have
-      additional columns, too).  The columns must have matching data types,
-      and if they have <literal>NOT NULL</literal> constraints in the parent
-      then they must also have <literal>NOT NULL</literal> constraints in the
-      child.
+      additional columns, too).  The columns must have matching data types.
      </para>
 
      <para>
-      There must also be matching child-table constraints for all
-      <literal>CHECK</literal> constraints of the parent, except those
-      marked non-inheritable (that is, created with <literal>ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</literal>)
-      in the parent, which are ignored; all child-table constraints matched
-      must not be marked non-inheritable.
-      Currently
+      In addition, all <literal>CHECK</literal> and <literal>NOT NULL</literal>
+      constraints on the parent must also exist on the child, except those
+      marked non-inheritable (that is, created with
+      <literal>ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</literal>), which
+      are ignored.  All child-table constraints matched must not be marked
+      non-inheritable.  Currently
       <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>, and
       <literal>FOREIGN KEY</literal> constraints are not considered, but
       this might change in the future.
@@ -1793,11 +1791,17 @@ ALTER TABLE measurement
   <title>Compatibility</title>
 
   <para>
-   The forms <literal>ADD</literal> (without <literal>USING INDEX</literal>),
+   The forms <literal>ADD [COLUMN]</literal>,
    <literal>DROP [COLUMN]</literal>, <literal>DROP IDENTITY</literal>, <literal>RESTART</literal>,
    <literal>SET DEFAULT</literal>, <literal>SET DATA TYPE</literal> (without <literal>USING</literal>),
    <literal>SET GENERATED</literal>, and <literal>SET <replaceable>sequence_option</replaceable></literal>
-   conform with the SQL standard.  The other forms are
+   conform with the SQL standard.
+   The form <literal>ADD <replaceable>table_constraint</replaceable></literal>
+   conforms with the SQL standard when the <literal>USING INDEX</literal> and
+   <literal>NOT VALID</literal> clauses are omitted and the constraint type is
+   one of <literal>CHECK</literal>, <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>,
+   or <literal>REFERENCES</literal>.
+   The other forms are
    <productname>PostgreSQL</productname> extensions of the SQL standard.
    Also, the ability to specify more than one manipulation in a single
    <command>ALTER TABLE</command> command is an extension.

doc/src/sgml/ref/create_foreign_table.sgml

@@ -43,7 +43,7 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name
 <phrase>where <replaceable class="parameter">column_constraint</replaceable> is:</phrase>
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
-{ NOT NULL |
+{ NOT NULL [ NO INHERIT ] |
   NULL |
   CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
   DEFAULT <replaceable>default_expr</replaceable> |
@@ -52,6 +52,7 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name
 <phrase>and <replaceable class="parameter">table_constraint</replaceable> is:</phrase>
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
+  NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
 CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ]
 
 <phrase>and <replaceable class="parameter">partition_bound_spec</replaceable> is:</phrase>
@@ -203,11 +204,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry>
-    <term><literal>NOT NULL</literal></term>
+    <term><literal>NOT NULL</literal> [ NO INHERIT ]</term>
     <listitem>
      <para>
       The column is not allowed to contain null values.
      </para>
+
+     <para>
+      A constraint marked with <literal>NO INHERIT</literal> will not propagate to
+      child tables.
+     </para>
     </listitem>
    </varlistentry>
 

doc/src/sgml/ref/create_table.sgml

@@ -61,7 +61,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
 <phrase>where <replaceable class="parameter">column_constraint</replaceable> is:</phrase>
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
-{ NOT NULL |
+{ NOT NULL [ NO INHERIT ]  |
   NULL |
   CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
   DEFAULT <replaceable>default_expr</replaceable> |
@@ -77,6 +77,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
 
 [ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
 { CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
+  NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
   UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <replaceable class="parameter">index_parameters</replaceable> |
   PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] [, <replaceable class="parameter">column_name</replaceable> WITHOUT OVERLAPS ] ) <replaceable class="parameter">index_parameters</replaceable> |
   EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ] |
@@ -818,11 +819,16 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
    </varlistentry>
 
    <varlistentry id="sql-createtable-parms-not-null">
-    <term><literal>NOT NULL</literal></term>
+    <term><literal>NOT NULL [ NO INHERIT ] </literal></term>
     <listitem>
      <para>
       The column is not allowed to contain null values.
      </para>
+
+     <para>
+      A constraint marked with <literal>NO INHERIT</literal> will not propagate to
+      child tables.
+     </para>
     </listitem>
    </varlistentry>
 
@@ -2398,13 +2404,6 @@ CREATE TABLE cities_partdef
     constraint, and index names must be unique across all relations within
     the same schema.
    </para>
-
-   <para>
-    Currently, <productname>PostgreSQL</productname> does not record names
-    for not-null constraints at all, so they are not
-    subject to the uniqueness restriction.  This might change in a future
-    release.
-   </para>
   </refsect2>
 
   <refsect2>