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doc: Clarify not-null constraints in information schema 

Add a bit of clarification in various places that not-null constraints
are included under check constraints in the information schema.
This commit is contained in:
Peter Eisentraut 2023-10-04 15:03:48 +02:00
parent 3338a98382
commit af2324fabf
1 changed files with 11 additions and 2 deletions
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13
doc/src/sgml/information_schema.sgml
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@ -917,6 +917,13 @@
domain is the owner of the constraint.)
</para>
<para>
The SQL standard considers not-null constraints to be check constraints
with a <literal>CHECK (<replaceable>column_name</replaceable> IS NOT
NULL)</literal> expression. So not-null constraints are also included here
and don't have a separate view.
</para>
<table>
<title><structname>check_constraints</structname> Columns</title>
<tgroup cols="1">
@ -2116,7 +2123,9 @@
columns in the current database that are used by some constraint.
Only those columns are shown that are contained in a table owned by
a currently enabled role. For a check constraint, this view
identifies the columns that are used in the check expression. For
identifies the columns that are used in the check expression. For a
not-null constraint, this view identifies the column that the constraint is
defined on. For
a foreign key constraint, this view identifies the columns that the
foreign key references. For a unique or primary key constraint,
this view identifies the constrained columns.
@ -6856,7 +6865,7 @@ ORDER BY c.ordinal_position;
<structfield>constraint_type</structfield> <type>character_data</type>
</para>
<para>
Type of the constraint: <literal>CHECK</literal>,
Type of the constraint: <literal>CHECK</literal> (includes not-null constraints),
<literal>FOREIGN KEY</literal>, <literal>PRIMARY KEY</literal>,
or <literal>UNIQUE</literal>
</para></entry>