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PostgreSQL 8.2.6 Documentation | ||||
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Table 9-40 shows several functions that extract session and system information.
Table 9-40. Session Information Functions
Name | Return Type | Description |
---|---|---|
current_database () | name | name of current database |
current_schema () | name | name of current schema |
current_schemas (boolean) | name[] | names of schemas in search path optionally including implicit schemas |
current_user | name | user name of current execution context |
inet_client_addr () | inet | address of the remote connection |
inet_client_port () | int | port of the remote connection |
inet_server_addr () | inet | address of the local connection |
inet_server_port () | int | port of the local connection |
pg_my_temp_schema () | oid | OID of session's temporary schema, or 0 if none |
pg_is_other_temp_schema (oid) | boolean | is schema another session's temporary schema? |
pg_postmaster_start_time () | timestamp with time zone | server start time |
session_user | name | session user name |
user | name | equivalent to current_user |
version () | text | PostgreSQL version information |
The session_user
is normally the user who initiated
the current database connection; but superusers can change this setting
with SET SESSION AUTHORIZATION.
The current_user
is the user identifier
that is applicable for permission checking. Normally, it is equal
to the session user, but it can be changed with
SET ROLE.
It also changes during the execution of
functions with the attribute SECURITY DEFINER.
In Unix parlance, the session user is the "real user" and
the current user is the "effective user".
Note:
current_user
,session_user
, anduser
have special syntactic status in SQL: they must be called without trailing parentheses.
current_schema
returns the name of the schema that is
at the front of the search path (or a null value if the search path is
empty). This is the schema that will be used for any tables or
other named objects that are created without specifying a target schema.
current_schemas(boolean)
returns an array of the names of all
schemas presently in the search path. The Boolean option determines whether or not
implicitly included system schemas such as pg_catalog are included in the search
path returned.
Note: The search path may be altered at run time. The command is:
SET search_path TO schema [, schema, ...]
inet_client_addr
returns the IP address of the
current client, and inet_client_port
returns the
port number.
inet_server_addr
returns the IP address on which
the server accepted the current connection, and
inet_server_port
returns the port number.
All these functions return NULL if the current connection is via a
Unix-domain socket.
pg_my_temp_schema
returns the OID of the current
session's temporary schema, or 0 if it has none (because it has not
created any temporary tables).
pg_is_other_temp_schema
returns true if the
given OID is the OID of any other session's temporary schema.
(This can be useful, for example, to exclude other sessions' temporary
tables from a catalog display.)
pg_postmaster_start_time
returns the
timestamp with time zone when the
server started.
version
returns a string describing the
PostgreSQL server's version.
Table 9-41 lists functions that allow the user to query object access privileges programmatically. See Section 5.6 for more information about privileges.
Table 9-41. Access Privilege Inquiry Functions
Name | Return Type | Description |
---|---|---|
has_database_privilege (user,
database,
privilege)
| boolean | does user have privilege for database |
has_database_privilege (database,
privilege)
| boolean | does current user have privilege for database |
has_function_privilege (user,
function,
privilege)
| boolean | does user have privilege for function |
has_function_privilege (function,
privilege)
| boolean | does current user have privilege for function |
has_language_privilege (user,
language,
privilege)
| boolean | does user have privilege for language |
has_language_privilege (language,
privilege)
| boolean | does current user have privilege for language |
has_schema_privilege (user,
schema,
privilege)
| boolean | does user have privilege for schema |
has_schema_privilege (schema,
privilege)
| boolean | does current user have privilege for schema |
has_table_privilege (user,
table,
privilege)
| boolean | does user have privilege for table |
has_table_privilege (table,
privilege)
| boolean | does current user have privilege for table |
has_tablespace_privilege (user,
tablespace,
privilege)
| boolean | does user have privilege for tablespace |
has_tablespace_privilege (tablespace,
privilege)
| boolean | does current user have privilege for tablespace |
pg_has_role (user,
role,
privilege)
| boolean | does user have privilege for role |
pg_has_role (role,
privilege)
| boolean | does current user have privilege for role |
has_database_privilege
checks whether a user
can access a database in a particular way. The possibilities for its
arguments are analogous to has_table_privilege
.
The desired access privilege type must evaluate to
CREATE,
CONNECT,
TEMPORARY, or
TEMP (which is equivalent to
TEMPORARY).
has_function_privilege
checks whether a user
can access a function in a particular way. The possibilities for its
arguments are analogous to has_table_privilege
.
When specifying a function by a text string rather than by OID,
the allowed input is the same as for the regprocedure data type
(see Section 8.12).
The desired access privilege type must evaluate to
EXECUTE.
An example is:
SELECT has_function_privilege('joeuser', 'myfunc(int, text)', 'execute');
has_language_privilege
checks whether a user
can access a procedural language in a particular way. The possibilities
for its arguments are analogous to has_table_privilege
.
The desired access privilege type must evaluate to
USAGE.
has_schema_privilege
checks whether a user
can access a schema in a particular way. The possibilities for its
arguments are analogous to has_table_privilege
.
The desired access privilege type must evaluate to
CREATE or
USAGE.
has_table_privilege
checks whether a user
can access a table in a particular way. The user can be
specified by name or by OID
(pg_authid.oid), or if the argument is
omitted
current_user
is assumed. The table can be specified
by name or by OID. (Thus, there are actually six variants of
has_table_privilege
, which can be distinguished by
the number and types of their arguments.) When specifying by name,
the name can be schema-qualified if necessary.
The desired access privilege type
is specified by a text string, which must evaluate to one of the
values SELECT, INSERT,
UPDATE, DELETE,
REFERENCES, or TRIGGER.
(Case of the string is not significant, however.)
An example is:
SELECT has_table_privilege('myschema.mytable', 'select');
has_tablespace_privilege
checks whether a user
can access a tablespace in a particular way. The possibilities for its
arguments are analogous to has_table_privilege
.
The desired access privilege type must evaluate to
CREATE.
pg_has_role
checks whether a user
can access a role in a particular way. The possibilities for its
arguments are analogous to has_table_privilege
.
The desired access privilege type must evaluate to
MEMBER or
USAGE.
MEMBER denotes direct or indirect membership in
the role (that is, the right to do SET ROLE), while
USAGE denotes whether the privileges of the role
are immediately available without doing SET ROLE.
To test whether a user holds a grant option on the privilege, append WITH GRANT OPTION to the privilege key word; for example 'UPDATE WITH GRANT OPTION'.
Table 9-42 shows functions that determine whether a certain object is visible in the current schema search path. A table is said to be visible if its containing schema is in the search path and no table of the same name appears earlier in the search path. This is equivalent to the statement that the table can be referenced by name without explicit schema qualification. For example, to list the names of all visible tables:
SELECT relname FROM pg_class WHERE pg_table_is_visible(oid);
Table 9-42. Schema Visibility Inquiry Functions
Name | Return Type | Description |
---|---|---|
pg_conversion_is_visible (conversion_oid)
| boolean | is conversion visible in search path |
pg_function_is_visible (function_oid)
| boolean | is function visible in search path |
pg_operator_is_visible (operator_oid)
| boolean | is operator visible in search path |
pg_opclass_is_visible (opclass_oid)
| boolean | is operator class visible in search path |
pg_table_is_visible (table_oid)
| boolean | is table visible in search path |
pg_type_is_visible (type_oid)
| boolean | is type (or domain) visible in search path |
pg_conversion_is_visible
,
pg_function_is_visible
,
pg_operator_is_visible
,
pg_opclass_is_visible
,
pg_table_is_visible
, and
pg_type_is_visible
perform the visibility check for
conversions, functions, operators, operator classes, tables, and
types. Note that pg_table_is_visible
can also be used
with views, indexes and sequences; pg_type_is_visible
can also be used with domains. For functions and operators, an object in
the search path is visible if there is no object of the same name
and argument data type(s) earlier in the path. For operator
classes, both name and associated index access method are considered.
All these functions require object OIDs to identify the object to be checked. If you want to test an object by name, it is convenient to use the OID alias types (regclass, regtype, regprocedure, or regoperator), for example
SELECT pg_type_is_visible('myschema.widget'::regtype);
Note that it would not make much sense to test an unqualified name in this way — if the name can be recognized at all, it must be visible.
Table 9-43 lists functions that extract information from the system catalogs.
Table 9-43. System Catalog Information Functions
Name | Return Type | Description |
---|---|---|
format_type (type_oid, typemod) | text | get SQL name of a data type |
pg_get_constraintdef (constraint_oid) | text | get definition of a constraint |
pg_get_constraintdef (constraint_oid, pretty_bool) | text | get definition of a constraint |
pg_get_expr (expr_text, relation_oid) | text | decompile internal form of an expression, assuming that any Vars in it refer to the relation indicated by the second parameter |
pg_get_expr (expr_text, relation_oid, pretty_bool) | text | decompile internal form of an expression, assuming that any Vars in it refer to the relation indicated by the second parameter |
pg_get_indexdef (index_oid) | text | get CREATE INDEX command for index |
pg_get_indexdef (index_oid, column_no, pretty_bool) | text | get CREATE INDEX command for index, or definition of just one index column when column_no is not zero |
pg_get_ruledef (rule_oid) | text | get CREATE RULE command for rule |
pg_get_ruledef (rule_oid, pretty_bool) | text | get CREATE RULE command for rule |
pg_get_serial_sequence (table_name, column_name) | text | get name of the sequence that a serial or bigserial column uses |
pg_get_triggerdef (trigger_oid) | text | get CREATE [ CONSTRAINT ] TRIGGER command for trigger |
pg_get_userbyid (roleid) | name | get role name with given ID |
pg_get_viewdef (view_name) | text | get underlying SELECT command for view (deprecated) |
pg_get_viewdef (view_name, pretty_bool) | text | get underlying SELECT command for view (deprecated) |
pg_get_viewdef (view_oid) | text | get underlying SELECT command for view |
pg_get_viewdef (view_oid, pretty_bool) | text | get underlying SELECT command for view |
pg_tablespace_databases (tablespace_oid) | setof oid | get the set of database OIDs that have objects in the tablespace |
format_type
returns the SQL name of a data type that
is identified by its type OID and possibly a type modifier. Pass NULL
for the type modifier if no specific modifier is known.
pg_get_constraintdef
,
pg_get_indexdef
, pg_get_ruledef
,
and pg_get_triggerdef
, respectively reconstruct the
creating command for a constraint, index, rule, or trigger. (Note that this
is a decompiled reconstruction, not the original text of the command.)
pg_get_expr
decompiles the internal form of an
individual expression, such as the default value for a column. It may be
useful when examining the contents of system catalogs.
pg_get_viewdef
reconstructs the SELECT
query that defines a view. Most of these functions come in two variants,
one of which can optionally "pretty-print" the result. The
pretty-printed format is more readable, but the default format is more
likely to be interpreted the same way by future versions of
PostgreSQL; avoid using pretty-printed output for dump
purposes. Passing false for the pretty-print parameter yields
the same result as the variant that does not have the parameter at all.
pg_get_serial_sequence
returns the name of the
sequence associated with a column, or NULL if no sequence is associated
with the column. The first input parameter is a table name with
optional schema, and the second parameter is a column name. Because
the first parameter is potentially a schema and table, it is not treated
as a double-quoted identifier, meaning it is lowercased by default,
while the second parameter, being just a column name, is treated as
double-quoted and has its case preserved. The function returns a value
suitably formatted for passing to the sequence functions (see Section 9.12). This association can be modified or
removed with ALTER SEQUENCE OWNED BY. (The function
probably should have been called
pg_get_owned_sequence
; its name reflects the fact
that it's typically used with serial or bigserial
columns.)
pg_get_userbyid
extracts a role's name given
its OID.
pg_tablespace_databases
allows a tablespace to be
examined. It returns the set of OIDs of databases that have objects stored
in the tablespace. If this function returns any rows, the tablespace is not
empty and cannot be dropped. To display the specific objects populating the
tablespace, you will need to connect to the databases identified by
pg_tablespace_databases
and query their
pg_class catalogs.
The functions shown in Table 9-44 extract comments previously stored with the COMMENT command. A null value is returned if no comment could be found matching the specified parameters.
Table 9-44. Comment Information Functions
Name | Return Type | Description |
---|---|---|
col_description (table_oid, column_number) | text | get comment for a table column |
obj_description (object_oid, catalog_name) | text | get comment for a database object |
obj_description (object_oid) | text | get comment for a database object (deprecated) |
shobj_description (object_oid, catalog_name) | text | get comment for a shared database object |
col_description
returns the comment for a table column,
which is specified by the OID of its table and its column number.
obj_description
cannot be used for table columns since
columns do not have OIDs of their own.
The two-parameter form of obj_description
returns the
comment for a database object specified by its OID and the name of the
containing system catalog. For example,
obj_description(123456,'pg_class')
would retrieve the comment for a table with OID 123456.
The one-parameter form of obj_description
requires only
the object OID. It is now deprecated since there is no guarantee that
OIDs are unique across different system catalogs; therefore, the wrong
comment could be returned.
shobj_description
is used just like
obj_description
only that it is used for retrieving
comments on shared objects. Some system catalogs are global to all
databases within each cluster and their descriptions are stored globally
as well.