PostgreSQL Chinese Learning Manual (system table)

I. pg_class:

The system table records metadata of data tables, indexes (still need to see pg_index), sequences, views, composite types, and some special link types. Note: not all fields make sense for all object types.

Name	Type	Reference	Description
Relname	Name		Data Type name.
Relnamespace	Oid	Pg_namespace.oid	OI that contains the namespace (mode) of this object.
Reltype	Oid	Pg_type.oid	The data type corresponding to the row type of this table.
Relowner	Oid	Pg_authid.oid	The owner of the object.
Relam	Oid	Pg_am.oid	The index object indicates the index type (B-tree, hash ).
Relfilenode	Oid		The name of the file where the object is stored on the disk. If not, it is 0.
Reltablespace	Oid	Pg_tablespace.oid	The tablespace where the object is located. If the value is zero, the default tablespace of the database is used. (This field makes no sense if the object has no files on the disk)
Relpages	Int4		The number of disk pages occupied by the data table or index. The query planner selects the optimal path with this value.
Reltuples	Float4		The number of rows in the table. This value is only an estimate used by the scheduler.
Reltoastrelid	Oid	Pg_class.oid	OID of the TOAST table associated with this table, if not 0. The TOAST table stores large fields offline in a subordinate table.
Reltoastidxid	Oid	Pg_class.oid	If it is a TOAST table, this field is the OID of its index, and if it is not a TOAST table, it is 0.
Relhasindex	Bool		If this is a data table with at least (or recently) One index, it is true. It is set by create index, but drop index does not immediately clear it. If VACUUM finds that a table has no index, it clears relhasindex.
Relisshared	Bool		True if the table is shared by all databases in the cluster.
Relkind	Char		R = normal table, I = index, S = sequence, v = view, c = composite type, s = Special, t = TOAST table
Relnatts	Int2		Number of user fields in the data table (excluding system fields, such as oid ). The pg_attribute is bound to have the same number of data rows. See pg_attribute.attnum.
Relchecks	Int2		Check the number of constraints in the table. For more information, see pg_constraint.
Reltriggers	Int2		Number of triggers in the table. For more information, see pg_trigger.
Relhasoids	Bool		If we generate an OID for each row of the object, it is true.
Relhaspkey	Bool		If the table has a primary key, it is true.
Relhasrules	Bool		If the table has rules, it will be true. SeePg_rewriteTable.
Relhassubclass	Bool		If the table has a sub-table, it is true.
Relacl	Aclitem []		Access permission.

See the following application example:
# View the mode of the specified table object testtable
Postgres = # SELECT relname, relnamespace, nspname FROM pg_class c, pg_namespace n WHERE relname = 'testtable' AND relnamespace = n. oid;
Relname | relnamespace | nspname
------------- + -------------- + ---------
Testtable | 2200 | public
(1 row)
# View the owner (role) of the specified table object testtable ).
Postgres = # select relname, rolname from pg_class c, pg_authid au where relname = 'testtable' and relowner = au. oid;
Relname | rolname
------------- + ----------
Testtable | postgres
(1 row)

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