GRANT

Description

The GRANT command has two basic variants: one that grants privileges on a database object (table, view, sequence, database, function, procedural language, schema, or tablespace), and one that grants membership in a role. These variants are similar in many ways, but they are different enough to be described separately.

As of PostgreSQL 8.1, the concepts of users and groups have been unified into a single kind of entity called a role. It is therefore no longer necessary to use the keyword GROUP to identify whether a grantee is a user or a group. GROUP is still allowed in the command, but it is a noise word.

Notes

The REVOKE command is used to revoke access privileges.

When a non-owner of an object attempts to GRANT privileges on the object, the command will fail outright if the user has no privileges whatsoever on the object. As long as some privilege is available, the command will proceed, but it will grant only those privileges for which the user has grant options. The GRANT ALL PRIVILEGES forms will issue a warning message if no grant options are held, while the other forms will issue a warning if grant options for any of the privileges specifically named in the command are not held. (In principle these statements apply to the object owner as well, but since the owner is always treated as holding all grant options, the cases can never occur.)

It should be noted that database superusers can access all objects regardless of object privilege settings. This is comparable to the rights of root in a Unix system. As with root, it's unwise to operate as a superuser except when absolutely necessary.

If a superuser chooses to issue a GRANT or REVOKE command, the command is performed as though it were issued by the owner of the affected object. In particular, privileges granted via such a command will appear to have been granted by the object owner. (For role membership, the membership appears to have been granted by the containing role itself.)

GRANT and REVOKE can also be done by a role that is not the owner of the affected object, but is a member of the role that owns the object, or is a member of a role that holds privileges WITH GRANT OPTION on the object. In this case the privileges will be recorded as having been granted by the role that actually owns the object or holds the privileges WITH GRANT OPTION. For example, if table t1 is owned by role g1, of which role u1 is a member, then u1 can grant privileges on t1 to u2, but those privileges will appear to have been granted directly by g1. Any other member of role g1 could revoke them later.

If the role executing GRANT holds the required privileges indirectly via more than one role membership path, it is unspecified which containing role will be recorded as having done the grant. In such cases it is best practice to use SET ROLE to become the specific role you want to do the GRANT as.

Currently, PostgreSQL does not support granting or revoking privileges for individual columns of a table. One possible workaround is to create a view having just the desired columns and then grant privileges to that view.

Use psql's \z command to obtain information about existing privileges, for example:

=> \z mytable

                        Access privileges for database "lusitania"
 Schema |  Name   | Type  |                     Access privileges
--------+---------+-------+------------------------------------------------------------
 public | mytable | table | {miriam=arwdRxt/miriam,=r/miriam,"group todos=arw/miriam"}
(1 row)

The entries shown by \z are interpreted thus:

              =xxxx -- privileges granted to PUBLIC
         uname=xxxx -- privileges granted to a user
   group gname=xxxx -- privileges granted to a group

                  r -- SELECT ("read")
                  w -- UPDATE ("write")
                  a -- INSERT ("append")
                  d -- DELETE
                  R -- RULE
                  x -- REFERENCES
                  t -- TRIGGER
                  X -- EXECUTE
                  U -- USAGE
                  C -- CREATE
                  T -- TEMPORARY
            arwdRxt -- ALL PRIVILEGES (for tables)
                  * -- grant option for preceding privilege

              /yyyy -- user who granted this privilege

The above example display would be seen by user miriam after creating table mytable and doing

GRANT SELECT ON mytable TO PUBLIC;
GRANT SELECT, UPDATE, INSERT ON mytable TO GROUP todos;

If the "Access privileges" column is empty for a given object, it means the object has default privileges (that is, its privileges column is null). Default privileges always include all privileges for the owner, and may 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=arwdRxt/miriam}) and then modify them per the specified request.

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.

Examples

Grant insert privilege to all users on table films:

GRANT INSERT ON films TO PUBLIC;

Grant all available privileges to user manuel on view kinds:

GRANT ALL PRIVILEGES ON kinds TO manuel;

Note that while the above will indeed grant all privileges if executed by a superuser or the owner of kinds, when executed by someone else it will only grant those permissions for which the someone else has grant options.

Grant membership in role admins to user joe:

GRANT admins TO joe;

Compatibility

According to the SQL standard, the PRIVILEGES key word in ALL PRIVILEGES is required. The SQL standard does not support setting the privileges on more than one object per command.

PostgreSQL allows an object owner to revoke his own ordinary privileges: for example, a table owner can make the table read-only to himself by revoking his own INSERT, UPDATE, and DELETE privileges. This is not possible according to the SQL standard. The reason is that PostgreSQL treats the owner's privileges as having been granted by the owner to himself; therefore he can revoke them too. In the SQL standard, the owner's privileges are granted by an assumed entity "_SYSTEM". Not being "_SYSTEM", the owner cannot revoke these rights.

The SQL standard allows setting privileges for individual columns within a table:

GRANT privileges
    ON table [ ( column [, ...] ) ] [, ...]
    TO { PUBLIC | username [, ...] } [ WITH GRANT OPTION ]

The SQL standard provides for a USAGE privilege on other kinds of objects: character sets, collations, translations, domains.

The RULE privilege, and privileges on databases, tablespaces, schemas, languages, and sequences are PostgreSQL extensions.

See Also

REVOKE