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Documentation of the system catalogs, directed toward PostgreSQL developers

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$Header: /cvsroot/pgsql/doc/src/sgml/catalogs.sgml,v 2.55 2002/08/28 15:02:55 tgl Exp $

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<chapter id="catalogs">

<title>pg_class</title>

<para>

<structname>pg_class</structname> catalogs tables andmostly

<structname>pg_class</structname> catalogs tables andmost

everything else that has columns or is otherwise similar to a

table. This includes indexes (but see also

<structname>pg_index</structname>), sequences, views, and some

kinds of special relation. Below, when we mean all of these

kinds of special relation; see <structfield>relkind</>.

. Below, when we mean all of these

kinds of objects we speak of <quote>relations</quote>. Not all

fields are meaningful for all relation types.

</para>

<entry>relfilenode</entry>

<entry><type>oid</type></entry>

<entry></entry>

<entry>Name of the on-disk file of this relation</entry>

<entry>Name of the on-disk file of this relation; 0 if none</entry>

</row>

<row>

<entry></entry>

<entry>

'r' = ordinary table, 'i' = index, 'S' = sequence, 'v' = view,

's' = special, 't' = secondary TOAST table

'c' = composite type, 's' = special, 't' = TOAST table

</entry>

</row>

<para>

This catalog stores information about data types. Scalar types

(<quote>base types</>) are created with <command>CREATE TYPE</command>.

A complex type isalso created for each table in the database, to

A complex type isautomatically created for each table in the database, to

represent the row structure of the table. It is also possible to create

complex types with <command>CREATE TYPE AS</command>, and

derived types with <command>CREATE DOMAIN</command>.

</para>

<entry>

If this is a complex type (see

<structfield>typtype</structfield>), then this field points to

the <structfield>pg_class</structfield> entry that defines the

corresponding table. A table could theoretically be used as a

composite data type, but this is only partly functional.

the <structname>pg_class</structname> entry that defines the

corresponding table. (For a free-standing composite type, the

<structname>pg_class</structname> entry doesn't really represent

a table, but it is needed anyway for the type's

<structname>pg_attribute</structname> entries to link to.)

Zero for non-complex types.

</entry>

</row>