Tabela 9-40 shows several functions that extract session and system information.
Tabela 9-40. Session Information Functions
|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".
Nota: current_user, session_user, and user 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.
Nota: The search path may be altered at run time. The command is:SET search_path TO esquema [, esquema, ...]
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.
Tabela 9-41. Access Privilege Inquiry Functions
|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 Seção 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'.
Tabela 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);
Tabela 9-42. Schema Visibility Inquiry Functions
|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
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.
Tabela 9-43 lists functions that extract information from the system catalogs.
Tabela 9-43. System Catalog Information Functions
|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 fetches the name of the sequence associated with a column, or NULL if there is no sequence associated with the column. The result is suitably formatted for passing to the sequence functions (see Seção 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.
Tabela 9-44. Comment Information Functions
|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.