When an object is created, it is assigned an owner. The owner is normally the role that executed the creation statement. For most kinds of objects, the initial state is that only the owner (or a superuser) can do anything with the object. To allow other roles to use it, privileges must be granted.
There are different kinds of privileges: SELECT
,
INSERT
, UPDATE
, DELETE
,
TRUNCATE
, REFERENCES
, TRIGGER
,
CREATE
, CONNECT
, TEMPORARY
,
EXECUTE
, and USAGE
.
The privileges applicable to a particular
object vary depending on the object's type (table, function, etc).
More detail about the meanings of these privileges appears below.
The following sections and chapters will also show you how
these privileges are used.
The right to modify or destroy an object is inherent in being the object's owner, and cannot be granted or revoked in itself. (However, like all privileges, that right can be inherited by members of the owning role; see Section 19.3.)
An object can be assigned to a new owner with an ALTER
command of the appropriate kind for the object, for example
ALTER TABLEtable_name
OWNER TOnew_owner
;
Superusers can always do this; ordinary roles can only do it if they are both the current owner of the object (or a member of the owning role) and a member of the new owning role.
To assign privileges, the GRANT command is
used. For example, if joe
is an existing role, and
accounts
is an existing table, the privilege to
update the table can be granted with:
GRANT UPDATE ON accounts TO joe;
Writing ALL
in place of a specific privilege grants all
privileges that are relevant for the object type.
The special “role” name PUBLIC
can
be used to grant a privilege to every role on the system. Also,
“group” roles can be set up to help manage privileges when
there are many users of a database — for details see
Chapter 19.
To revoke a previously-granted privilege, use the fittingly named REVOKE command:
REVOKE ALL ON accounts FROM PUBLIC;
Ordinarily, only the object's owner (or a superuser) can grant or revoke privileges on an object. However, it is possible to grant a privilege “with grant option”, which gives the recipient the right to grant it in turn to others. If the grant option is subsequently revoked then all who received the privilege from that recipient (directly or through a chain of grants) will lose the privilege. For details see the GRANT and REVOKE reference pages.
An object's owner can choose to revoke their own ordinary privileges, for example to make a table read-only for themselves as well as others. But owners are always treated as holding all grant options, so they can always re-grant their own privileges.
The available privileges are:
SELECT
Allows SELECT from
any column, or specific column(s), of a table, view, materialized
view, or other table-like object.
Also allows use of COPY TO.
This privilege is also needed to reference existing column values in
UPDATE or DELETE.
For sequences, this privilege also allows use of the
currval
function.
For large objects, this privilege allows the object to be read.
INSERT
Allows INSERT of a new row into a table, view,
etc. Can be granted on specific column(s), in which case
only those columns may be assigned to in the INSERT
command (other columns will therefore receive default values).
Also allows use of COPY FROM.
UPDATE
Allows UPDATE of any
column, or specific column(s), of a table, view, etc.
(In practice, any nontrivial UPDATE
command will
require SELECT
privilege as well, since it must
reference table columns to determine which rows to update, and/or to
compute new values for columns.)
SELECT ... FOR UPDATE
and SELECT ... FOR SHARE
also require this privilege on at least one column, in addition to the
SELECT
privilege. For sequences, this
privilege allows use of the nextval
and
setval
functions.
For large objects, this privilege allows writing or truncating the
object.
DELETE
Allows DELETE of a row from a table, view, etc.
(In practice, any nontrivial DELETE
command will
require SELECT
privilege as well, since it must
reference table columns to determine which rows to delete.)
TRUNCATE
Allows TRUNCATE on a table.
REFERENCES
Allows creation of a foreign key constraint referencing a table, or specific column(s) of a table.
TRIGGER
Allows creation of a trigger on a table, view, etc.
CREATE
For databases, allows new schemas and publications to be created within the database, and allows trusted extensions to be installed within the database.
For schemas, allows new objects to be created within the schema. To rename an existing object, you must own the object and have this privilege for the containing schema.
For tablespaces, allows tables, indexes, and temporary files to be created within the tablespace, and allows databases to be created that have the tablespace as their default tablespace.
Note that revoking this privilege will not alter the existence or location of existing objects.
CONNECT
Allows the grantee to connect to the database. This
privilege is checked at connection startup (in addition to checking
any restrictions imposed by lt_hba.conf
).
TEMPORARY
Allows temporary tables to be created while using the database.
EXECUTE
Allows calling a function or procedure, including use of any operators that are implemented on top of the function. This is the only type of privilege that is applicable to functions and procedures.
USAGE
For procedural languages, allows use of the language for the creation of functions in that language. This is the only type of privilege that is applicable to procedural languages.
For schemas, allows access to objects contained in the schema (assuming that the objects' own privilege requirements are also met). Essentially this allows the grantee to “look up” objects within the schema. Without this permission, it is still possible to see the object names, e.g., by querying system catalogs. Also, after revoking this permission, existing sessions might have statements that have previously performed this lookup, so this is not a completely secure way to prevent object access.
For sequences, allows use of the
currval
and nextval
functions.
For types and domains, allows use of the type or domain in the creation of tables, functions, and other schema objects. (Note that this privilege does not control all “usage” of the type, such as values of the type appearing in queries. It only prevents objects from being created that depend on the type. The main purpose of this privilege is controlling which users can create dependencies on a type, which could prevent the owner from changing the type later.)
For foreign-data wrappers, allows creation of new servers using the foreign-data wrapper.
For foreign servers, allows creation of foreign tables using the server. Grantees may also create, alter, or drop their own user mappings associated with that server.
The privileges required by other commands are listed on the reference page of the respective command.
LightDB grants privileges on some types of objects to
PUBLIC
by default when the objects are created.
No privileges are granted to PUBLIC
by default on
tables,
table columns,
sequences,
foreign data wrappers,
foreign servers,
large objects,
schemas,
or tablespaces.
For other types of objects, the default privileges
granted to PUBLIC
are as follows:
CONNECT
and TEMPORARY
(create
temporary tables) privileges for databases;
EXECUTE
privilege for functions and procedures; and
USAGE
privilege for languages and data types
(including domains).
The object owner can, of course, REVOKE
both default and expressly granted privileges. (For maximum
security, issue the REVOKE
in the same transaction that
creates the object; then there is no window in which another user
can use the object.)
Also, these default privilege settings can be overridden using the
ALTER DEFAULT PRIVILEGES command.
Table 5.1 shows the one-letter abbreviations that are used for these privilege types in ACL (Access Control List) values. You will see these letters in the output of the ltsql commands listed below, or when looking at ACL columns of system catalogs.
Table 5.1. ACL Privilege Abbreviations
Privilege | Abbreviation | Applicable Object Types |
---|---|---|
SELECT | r (“read”) |
LARGE OBJECT ,
SEQUENCE ,
TABLE (and table-like objects),
table column
|
INSERT | a (“append”) | TABLE , table column |
UPDATE | w (“write”) |
LARGE OBJECT ,
SEQUENCE ,
TABLE ,
table column
|
DELETE | d | TABLE |
TRUNCATE | D | TABLE |
REFERENCES | x | TABLE , table column |
TRIGGER | t | TABLE |
CREATE | C |
DATABASE ,
SCHEMA ,
TABLESPACE
|
CONNECT | c | DATABASE |
TEMPORARY | T | DATABASE |
EXECUTE | X | FUNCTION , PROCEDURE |
USAGE | U |
DOMAIN ,
FOREIGN DATA WRAPPER ,
FOREIGN SERVER ,
LANGUAGE ,
SCHEMA ,
SEQUENCE ,
TYPE
|
Table 5.2 summarizes the privileges available for each type of SQL object, using the abbreviations shown above. It also shows the ltsql command that can be used to examine privilege settings for each object type.
Table 5.2. Summary of Access Privileges
Object Type | All Privileges | Default PUBLIC Privileges | ltsql Command |
---|---|---|---|
DATABASE | CTc | Tc | \l |
DOMAIN | U | U | \dD+ |
FUNCTION or PROCEDURE | X | X | \df+ |
FOREIGN DATA WRAPPER | U | none | \dew+ |
FOREIGN SERVER | U | none | \des+ |
LANGUAGE | U | U | \dL+ |
LARGE OBJECT | rw | none | |
SCHEMA | UC | none | \dn+ |
SEQUENCE | rwU | none | \dp |
TABLE (and table-like objects) | arwdDxt | none | \dp |
Table column | arwx | none | \dp |
TABLESPACE | C | none | \db+ |
TYPE | U | U | \dT+ |
The privileges that have been granted for a particular object are
displayed as a list of aclitem
entries, where each
aclitem
describes the permissions of one grantee that
have been granted by a particular grantor. For example,
calvin=r*w/hobbes
specifies that the role
calvin
has the privilege
SELECT
(r
) with grant option
(*
) as well as the non-grantable
privilege UPDATE
(w
), both granted
by the role hobbes
. If calvin
also has some privileges on the same object granted by a different
grantor, those would appear as a separate aclitem
entry.
An empty grantee field in an aclitem
stands
for PUBLIC
.
As an example, suppose that user miriam
creates
table mytable
and does:
GRANT SELECT ON mytable TO PUBLIC; GRANT SELECT, UPDATE, INSERT ON mytable TO admin; GRANT SELECT (col1), UPDATE (col1) ON mytable TO miriam_rw;
Then ltsql's \dp
command
would show:
=> \dp mytable Access privileges Schema | Name | Type | Access privileges | Column privileges | Policies --------+---------+-------+-----------------------+-----------------------+---------- public | mytable | table | miriam=arwdDxt/miriam+| col1: +| | | | =r/miriam +| miriam_rw=rw/miriam | | | | admin=arw/miriam | | (1 row)
If the “Access privileges” column is empty for a given
object, it means the object has default privileges (that is, its
privileges entry in the relevant system catalog is null). Default
privileges always include all privileges for the owner, and can include
some privileges for PUBLIC
depending on the object
type, as explained above. The first GRANT
or REVOKE
on an object will instantiate the default
privileges (producing, for
example, miriam=arwdDxt/miriam
) and then modify them
per the specified request. Similarly, entries are shown in “Column
privileges” only for columns with nondefault privileges.
(Note: for this purpose, “default privileges” always means
the built-in default privileges for the object's type. An object whose
privileges have been affected by an ALTER DEFAULT
PRIVILEGES
command will always be shown with an explicit
privilege entry that includes the effects of
the ALTER
.)
Notice that the owner's implicit grant options are not marked in the
access privileges display. A *
will appear only when
grant options have been explicitly granted to someone.