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doc: Clarify not-null constraints in information schema

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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.) domain is the owner of the constraint.)
</para> </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> <table>
<title><structname>check_constraints</structname> Columns</title> <title><structname>check_constraints</structname> Columns</title>
<tgroup cols="1"> <tgroup cols="1">
@ -2116,7 +2123,9 @@
columns in the current database that are used by some constraint. columns in the current database that are used by some constraint.
Only those columns are shown that are contained in a table owned by Only those columns are shown that are contained in a table owned by
a currently enabled role. For a check constraint, this view 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 a foreign key constraint, this view identifies the columns that the
foreign key references. For a unique or primary key constraint, foreign key references. For a unique or primary key constraint,
this view identifies the constrained columns. this view identifies the constrained columns.
@ -6856,7 +6865,7 @@ ORDER BY c.ordinal_position;
<structfield>constraint_type</structfield> <type>character_data</type> <structfield>constraint_type</structfield> <type>character_data</type>
</para> </para>
<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>, <literal>FOREIGN KEY</literal>, <literal>PRIMARY KEY</literal>,
or <literal>UNIQUE</literal> or <literal>UNIQUE</literal>
</para></entry> </para></entry>