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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 e49ae8d. 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 (b0e96f3) 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 <[email protected]> Author: Bernd Helmle <[email protected]> Reviewed-by: 何建 (jian he) <[email protected]> Reviewed-by: 王刚 (Tender Wang) <[email protected]> Reviewed-by: Justin Pryzby <[email protected]> Reviewed-by: Peter Eisentraut <[email protected]> Reviewed-by: Dean Rasheed <[email protected]> Discussion: https://postgr.es/m/[email protected]
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‎contrib/sepgsql/expected/alter.out

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@@ -164,7 +164,6 @@ LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_re
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema.regtest_table_2.b" permissive=0
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ALTER TABLE regtest_table ALTER b DROP NOT NULL;
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema_2.regtest_table.b" permissive=0
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema.regtest_table_2.b" permissive=0
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ALTER TABLE regtest_table ALTER b SET STATISTICS -1;
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema_2.regtest_table.b" permissive=0
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema.regtest_table_2.b" permissive=0
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ALTER TABLE regtest_ptable ALTER p DROP NOT NULL;
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema_2.regtest_table_part.p" permissive=0
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema.regtest_ptable_1_tens.p" permissive=0
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ALTER TABLE regtest_ptable ALTER p SET STATISTICS -1;
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LOG: SELinux: allowed { setattr } scontext=unconfined_u:unconfined_r:sepgsql_regtest_superuser_t:s0 tcontext=unconfined_u:object_r:sepgsql_table_t:s0 tclass=db_column name="regtest_schema_2.regtest_table_part.p" permissive=0

‎contrib/test_decoding/expected/ddl.out

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@@ -492,6 +492,9 @@ WITH (user_catalog_table = true)
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options | text[] | | | | extended | |
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Indexes:
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"replication_metadata_pkey" PRIMARY KEY, btree (id)
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Not-null constraints:
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"replication_metadata_id_not_null" NOT NULL "id"
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"replication_metadata_relation_not_null" NOT NULL "relation"
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Options: user_catalog_table=true
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INSERT INTO replication_metadata(relation, options)
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options | text[] | | | | extended | |
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Indexes:
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"replication_metadata_pkey" PRIMARY KEY, btree (id)
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Not-null constraints:
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"replication_metadata_id_not_null" NOT NULL "id"
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"replication_metadata_relation_not_null" NOT NULL "relation"
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INSERT INTO replication_metadata(relation, options)
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VALUES ('bar', ARRAY['a', 'b']);
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options | text[] | | | | extended | |
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Indexes:
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"replication_metadata_pkey" PRIMARY KEY, btree (id)
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Not-null constraints:
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"replication_metadata_id_not_null" NOT NULL "id"
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"replication_metadata_relation_not_null" NOT NULL "relation"
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Options: user_catalog_table=true
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INSERT INTO replication_metadata(relation, options)
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rewritemeornot | integer | | | | plain | |
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Indexes:
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"replication_metadata_pkey" PRIMARY KEY, btree (id)
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Not-null constraints:
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"replication_metadata_id_not_null" NOT NULL "id"
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"replication_metadata_relation_not_null" NOT NULL "relation"
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Options: user_catalog_table=false
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INSERT INTO replication_metadata(relation, options)

‎doc/src/sgml/catalogs.sgml

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<structfield>attnotnull</structfield> <type>bool</type>
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</para>
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<para>
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This represents a not-null constraint.
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This column has a not-null constraint.
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</para></entry>
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</row>
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</indexterm>
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<para>
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The catalog <structname>pg_constraint</structname> stores check, primary
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key, unique, foreign key, and exclusion constraints on tables, as well as
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not-null constraints on domains.
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The catalog <structname>pg_constraint</structname> stores check, not-null,
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primary key, unique, foreign key, and exclusion constraints on tables.
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(Column constraints are not treated specially. Every column constraint is
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equivalent to some table constraint.)
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Not-null constraints on relations are represented in the
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<link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>
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catalog, not here.
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</para>
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<para>
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<para>
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<literal>c</literal> = check constraint,
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<literal>f</literal> = foreign key constraint,
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<literal>n</literal> = not-null constraint (domains only),
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<literal>n</literal> = not-null constraint,
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<literal>p</literal> = primary key constraint,
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<literal>u</literal> = unique constraint,
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<literal>t</literal> = constraint trigger,

‎doc/src/sgml/ddl.sgml

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@@ -772,17 +772,38 @@ CREATE TABLE products (
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price numeric
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);
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</programlisting>
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An explicit constraint name can also be specified, for example:
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<programlisting>
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CREATE TABLE products (
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product_no integer NOT NULL,
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name text <emphasis>CONSTRAINT products_name_not_null</emphasis> NOT NULL,
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price numeric
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);
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</programlisting>
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</para>
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<para>
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A not-null constraint is usually written as a column constraint. The
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syntax for writing it as a table constraint is
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<programlisting>
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CREATE TABLE products (
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product_no integer,
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name text,
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price numeric,
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<emphasis>NOT NULL product_no</emphasis>,
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<emphasis>NOT NULL name</emphasis>
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);
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</programlisting>
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But this syntax is not standard and mainly intended for use by
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<application>pg_dump</application>.
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</para>
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<para>
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A not-null constraint is always written as a column constraint. A
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not-null constraint is functionally equivalent to creating a check
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A not-null constraint is functionally equivalent to creating a check
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constraint <literal>CHECK (<replaceable>column_name</replaceable>
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IS NOT NULL)</literal>, but in
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<productname>PostgreSQL</productname> creating an explicit
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not-null constraint is more efficient. The drawback is that you
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cannot give explicit names to not-null constraints created this
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way.
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not-null constraint is more efficient.
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</para>
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<para>
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order the constraints are checked.
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</para>
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<para>
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However, a column can have at most one explicit not-null constraint.
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</para>
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<para>
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The <literal>NOT NULL</literal> constraint has an inverse: the
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<literal>NULL</literal> constraint. This does not mean that the
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<para>
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A table can have at most one primary key. (There can be any number
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of unique and not-null constraints, which are functionally almost the
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of unique constraints, which combined with not-null constraints are functionally almost the
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same thing, but only one can be identified as the primary key.)
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Relational database theory
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dictates that every table must have a primary key. This rule is
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ALTER TABLE products ADD CONSTRAINT some_name UNIQUE (product_no);
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ALTER TABLE products ADD FOREIGN KEY (product_group_id) REFERENCES product_groups;
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</programlisting>
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To add a not-null constraint, which cannot be written as a table
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constraint, use this syntax:
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</para>
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<para>
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To add a not-null constraint, which is normally not written as a table
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constraint, this special syntax is available:
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<programlisting>
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ALTER TABLE products ALTER COLUMN product_no SET NOT NULL;
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</programlisting>
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This command silently does nothing if the column already has a
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not-null constraint.
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</para>
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<para>
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</para>
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<para>
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This works the same for all constraint types except not-null
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constraints. To drop a not-null constraint use:
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Simplified syntax is available to drop a not-null constraint:
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<programlisting>
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ALTER TABLE products ALTER COLUMN product_no DROP NOT NULL;
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</programlisting>
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(Recall that not-null constraints do not have names.)
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This mirrors the <literal>SET NOT NULL</literal> syntax for adding a
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not-null constraint. This command will silently do nothing if the column
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does not have a not-null constraint. (Recall that a column can have at
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most one not-null constraint, so it is never ambiguous which constraint
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this command acts on.)
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</para>
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</sect2>
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<para>
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Both <literal>CHECK</literal> and <literal>NOT NULL</literal>
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constraints of a partitioned table are always inherited by all its
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partitions. <literal>CHECK</literal> constraints that are marked
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<literal>NO INHERIT</literal> are not allowed to be created on
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partitioned tables.
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You cannot drop a <literal>NOT NULL</literal> constraint on a
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partition's column if the same constraint is present in the parent
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table.
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partitions; it is not allowed to create <literal>NO INHERIT</literal>
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constraints of those types.
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You cannot drop a constraint of those types if the same constraint
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is present in the parent table.
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</para>
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</listitem>
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‎doc/src/sgml/ref/alter_foreign_table.sgml

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<para>
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This form adds a new constraint to a foreign table, using the same
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syntax as <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.
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Currently only <literal>CHECK</literal> constraints are supported.
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Currently only <literal>CHECK</literal> and <literal>NOT NULL</literal>
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constraints are supported.
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</para>
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179180
<para>
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182183
declares that some new condition should be assumed to hold for all rows
183184
in the foreign table. (See the discussion
184185
in <link linkend="sql-createforeigntable"><command>CREATE FOREIGN TABLE</command></link>.)
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If the constraint is marked <literal>NOT VALID</literal>, then it isn't
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If the constraint is marked <literal>NOT VALID</literal> (allowed only for
187+
the <literal>CHECK</literal> case), then it isn't
186188
assumed to hold, but is only recorded for possible future use.
187189
</para>
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</listitem>

‎doc/src/sgml/ref/alter_table.sgml

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<phrase>and <replaceable class="parameter">column_constraint</replaceable> is:</phrase>
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100100
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
101-
{ NOT NULL |
101+
{ NOT NULL [ NO INHERIT ] |
102102
NULL |
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CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
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DEFAULT <replaceable>default_expr</replaceable> |
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114114

115115
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
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{ CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
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NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
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UNIQUE [ NULLS [ NOT ] DISTINCT ] ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
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PRIMARY KEY ( <replaceable class="parameter">column_name</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> |
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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> ) ] |
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table. Subsequently, queries against the parent will include records
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of the target table. To be added as a child, the target table must
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already contain all the same columns as the parent (it could have
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additional columns, too). The columns must have matching data types,
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and if they have <literal>NOT NULL</literal> constraints in the parent
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then they must also have <literal>NOT NULL</literal> constraints in the
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child.
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additional columns, too). The columns must have matching data types.
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</para>
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<para>
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There must also be matching child-table constraints for all
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<literal>CHECK</literal> constraints of the parent, except those
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marked non-inheritable (that is, created with <literal>ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</literal>)
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in the parent, which are ignored; all child-table constraints matched
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must not be marked non-inheritable.
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Currently
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In addition, all <literal>CHECK</literal> and <literal>NOT NULL</literal>
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constraints on the parent must also exist on the child, except those
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marked non-inheritable (that is, created with
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<literal>ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT</literal>), which
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are ignored. All child-table constraints matched must not be marked
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non-inheritable. Currently
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<literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>, and
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<literal>FOREIGN KEY</literal> constraints are not considered, but
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this might change in the future.
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<title>Compatibility</title>
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17951793
<para>
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The forms <literal>ADD</literal> (without <literal>USING INDEX</literal>),
1794+
The forms <literal>ADD [COLUMN]</literal>,
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<literal>DROP [COLUMN]</literal>, <literal>DROP IDENTITY</literal>, <literal>RESTART</literal>,
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<literal>SET DEFAULT</literal>, <literal>SET DATA TYPE</literal> (without <literal>USING</literal>),
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<literal>SET GENERATED</literal>, and <literal>SET <replaceable>sequence_option</replaceable></literal>
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conform with the SQL standard. The other forms are
1798+
conform with the SQL standard.
1799+
The form <literal>ADD <replaceable>table_constraint</replaceable></literal>
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conforms with the SQL standard when the <literal>USING INDEX</literal> and
1801+
<literal>NOT VALID</literal> clauses are omitted and the constraint type is
1802+
one of <literal>CHECK</literal>, <literal>UNIQUE</literal>, <literal>PRIMARY KEY</literal>,
1803+
or <literal>REFERENCES</literal>.
1804+
The other forms are
18011805
<productname>PostgreSQL</productname> extensions of the SQL standard.
18021806
Also, the ability to specify more than one manipulation in a single
18031807
<command>ALTER TABLE</command> command is an extension.

‎doc/src/sgml/ref/create_foreign_table.sgml

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@@ -43,7 +43,7 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name
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4545
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
46-
{ NOT NULL |
46+
{ NOT NULL [ NO INHERIT ] |
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NULL |
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CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ] |
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DEFAULT <replaceable>default_expr</replaceable> |
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<phrase>and <replaceable class="parameter">table_constraint</replaceable> is:</phrase>
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5454
[ CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> ]
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NOT NULL <replaceable class="parameter">column_name</replaceable> [ NO INHERIT ] |
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CHECK ( <replaceable class="parameter">expression</replaceable> ) [ NO INHERIT ]
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5758
<phrase>and <replaceable class="parameter">partition_bound_spec</replaceable> is:</phrase>
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203204
</varlistentry>
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205206
<varlistentry>
206-
<term><literal>NOT NULL</literal></term>
207+
<term><literal>NOT NULL</literal> [ NO INHERIT ]</term>
207208
<listitem>
208209
<para>
209210
The column is not allowed to contain null values.
210211
</para>
212+
213+
<para>
214+
A constraint marked with <literal>NO INHERIT</literal> will not propagate to
215+
child tables.
216+
</para>
211217
</listitem>
212218
</varlistentry>
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