PostgreSQL SQL for Beginners

PostgreSQL tutorial for Beginners – PostgreSQL – PRIVILEGES

By on Thursday, June 3, 2021

PostgreSQL – PRIVILEGES

 

Whenever an object is created in a database, an owner is assigned to it. The owner is usually the one who executed the creation statement. For most kinds of objects, the initial state is that only the owner (or a superuser) can modify or delete the object. To allow other roles or users to use it, privileges or permission must be granted.

Different kinds of privileges in PostgreSQL are −

  • SELECT,
  • INSERT,
  • UPDATE,
  • DELETE,
  • TRUNCATE,
  • REFERENCES,
  • TRIGGER,
  • CREATE,
  • CONNECT,
  • TEMPORARY,
  • EXECUTE, and
  • USAGE

 

Depending on the type of the object (table, function, etc.,), privileges are applied to the object. To assign privileges to the users, the GRANT command is used.

Syntax for GRANT

Basic syntax for GRANT command is as follows −

GRANT privilege [, ...]
ON object [, ...]
TO { PUBLIC | GROUP group | username }
  • privilege − values could be: SELECT, INSERT, UPDATE, DELETE, RULE, ALL.
  • object − The name of an object to which to grant access. The possible objects are: table, view, sequence
  • PUBLIC − A short form representing all users.
  • GROUP group − A group to whom to grant privileges.
  • username − The name of a user to whom to grant privileges. PUBLIC is a short form representing all users.

 

The privileges can be revoked using the REVOKE command.

Syntax for REVOKE

Basic syntax for REVOKE command is as follows −

REVOKE privilege [, ...]
ON object [, ...]
FROM { PUBLIC | GROUP groupname | username }
  • privilege − values could be: SELECT, INSERT, UPDATE, DELETE, RULE, ALL.
  • object − The name of an object to which to grant access. The possible objects are: table, view, sequence
  • PUBLIC − A short form representing all users.
  • GROUP group − A group to whom to grant privileges.
  • username − The name of a user to whom to grant privileges. PUBLIC is a short form representing all users.

 

Example

To understand the privileges, let us first create a USER as follows −

testdb=# CREATE USER manisha WITH PASSWORD 'password';
CREATE ROLE

The message CREATE ROLE indicates that the USER “manisha” is created.

Consider the table COMPANY having records as follows −

testdb# select * from COMPANY;
 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Allen |  25 | Texas     |  15000
  3 | Teddy |  23 | Norway    |  20000
  4 | Mark  |  25 | Rich-Mond |  65000
  5 | David |  27 | Texas     |  85000
  6 | Kim   |  22 | South-Hall|  45000
  7 | James |  24 | Houston   |  10000
(7 rows)

Next, let us grant all privileges on a table COMPANY to the user “manisha” as follows −

testdb=# GRANT ALL ON COMPANY TO manisha;
GRANT

The message GRANT indicates that all privileges are assigned to the USER.

Next, let us revoke the privileges from the USER “manisha” as follows −

testdb=# REVOKE ALL ON COMPANY FROM manisha;
REVOKE

The message REVOKE indicates that all privileges are revoked from the USER.

You can even delete the user as follows −

testdb=# DROP USER manisha;
DROP ROLE

The message DROP ROLE indicates USER ‘Manisha’ is deleted from the database.

 

Python Example for Beginners

Two Machine Learning Fields

There are two sides to machine learning:

  • Practical Machine Learning:This is about querying databases, cleaning data, writing scripts to transform data and gluing algorithm and libraries together and writing custom code to squeeze reliable answers from data to satisfy difficult and ill defined questions. It’s the mess of reality.
  • Theoretical Machine Learning: This is about math and abstraction and idealized scenarios and limits and beauty and informing what is possible. It is a whole lot neater and cleaner and removed from the mess of reality.

 

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