| PostgreSQL 8.2.12 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, anduserhave 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.