GRANT and REVOKE permissions in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the GRANT command do in PostgreSQL?

The GRANT command gives specific permissions on database objects to users or roles, allowing them to perform certain actions like SELECT, INSERT, UPDATE, or DELETE.

beginner

What is the purpose of the REVOKE command?

The REVOKE command removes previously granted permissions from users or roles, preventing them from performing certain actions on database objects.

beginner

How do you grant SELECT permission on a table named 'employees' to a user named 'alice'?

Use the command:
GRANT SELECT ON employees TO alice;

beginner

How do you revoke INSERT permission on a table named 'sales' from a role named 'sales_team'?

Use the command:
REVOKE INSERT ON sales FROM sales_team;

intermediate

Can you grant multiple permissions at once using GRANT? How?

Yes, you can grant multiple permissions by listing them separated by commas. For example:
GRANT SELECT, INSERT ON orders TO bob;

Which command gives a user permission to read data from a table?

A GRANT SELECT ON table TO user;

B REVOKE SELECT ON table FROM user;

C GRANT DELETE ON table TO user;

D REVOKE INSERT ON table FROM user;

GRANT SELECT allows the user to read data from the table.

What does the REVOKE command do?

A Gives permissions to users

B Creates a new user

C Removes permissions from users

D Deletes a table

REVOKE removes permissions that were previously granted.

How would you remove UPDATE permission from user 'john' on table 'products'?

A GRANT UPDATE ON products TO john;

B REVOKE UPDATE ON products FROM john;

C DELETE UPDATE ON products FROM john;

D REMOVE UPDATE ON products FROM john;

REVOKE UPDATE ON products FROM john; removes the UPDATE permission.

Which of the following is a valid way to grant multiple permissions?

A GRANT SELECT, INSERT ON table TO user;

B GRANT SELECT INSERT ON table TO user;

C GRANT (SELECT, INSERT) ON table TO user;

D GRANT SELECT; INSERT ON table TO user;

Permissions are listed separated by commas without parentheses.

If you want to allow a user to add new rows to a table, which permission should you grant?

A SELECT

B DELETE

C UPDATE

D INSERT

INSERT permission allows adding new rows to a table.

Explain how to use GRANT and REVOKE commands to control user permissions on a PostgreSQL table.

Think about how you let or stop someone from doing things with your data.

Describe a real-life scenario where you would use GRANT and REVOKE in a database.

Imagine sharing a document with friends and then changing who can edit it.

Practice

1. What does the GRANT command do in PostgreSQL?

easy

A. It gives specific permissions to a user or role.

B. It deletes a user from the database.

C. It creates a new database.

D. It backs up the database.

Solution

1. Step 1: Understand the purpose of GRANT

   The GRANT command is used to give permissions like SELECT, INSERT, or UPDATE to users or roles.

2. Step 2: Compare with other options

   Deleting users, creating databases, or backing up are done by other commands, not GRANT.

3. Final Answer:

   It gives specific permissions to a user or role. -> Option A

4. Quick Check:

   GRANT = give permissions [OK]

Hint: GRANT means give rights; REVOKE means take away [OK]

Common Mistakes:

• Confusing GRANT with user creation
• Thinking GRANT deletes data
• Mixing GRANT with backup commands

2. Which of the following is the correct syntax to grant SELECT permission on table employees to user john?

easy

A. GRANT ON employees SELECT TO john;

B. GRANT john ON employees SELECT;

C. GRANT SELECT TO john ON employees;

D. GRANT SELECT ON employees TO john;

Solution

1. Step 1: Recall correct GRANT syntax

   The correct syntax is: GRANT permission ON object TO user;

2. Step 2: Match syntax with options

   GRANT SELECT ON employees TO john; matches the correct order: GRANT SELECT ON employees TO john;

3. Final Answer:

   GRANT SELECT ON employees TO john; -> Option D

4. Quick Check:

   GRANT + permission + ON + object + TO + user [OK]

Hint: GRANT permission ON object TO user; is the pattern [OK]

Common Mistakes:

• Mixing order of keywords
• Placing user before permission
• Omitting ON keyword

3. Given the commands:
GRANT SELECT ON customers TO alice;
REVOKE SELECT ON customers FROM alice;
What permissions does user alice have on table customers after these commands?

medium

A. Alice can SELECT from customers.

B. Alice can INSERT into customers.

C. Alice cannot SELECT from customers.

D. Alice has all permissions on customers.

Solution

1. Step 1: Analyze the GRANT command

   Alice is given SELECT permission on customers table.

2. Step 2: Analyze the REVOKE command

   The SELECT permission is then revoked from Alice, removing her ability to SELECT.

3. Final Answer:

   Alice cannot SELECT from customers. -> Option C

4. Quick Check:

   REVOKE removes permission given by GRANT [OK]

Hint: REVOKE removes permissions previously granted [OK]

Common Mistakes:

• Assuming REVOKE adds permissions
• Confusing SELECT with INSERT
• Ignoring the order of commands

4. Identify the error in the following command:
REVOKE ALL PRIVILEGES employees FROM bob;

medium

A. The order of keywords is incorrect.

B. The user name should be before the table name.

C. REVOKE cannot be used with ALL PRIVILEGES.

D. The command is correct.

Solution

1. Step 1: Check correct REVOKE syntax

   The correct syntax is: REVOKE privileges ON object FROM user;

2. Step 2: Compare with given command

   The command uses: REVOKE ALL PRIVILEGES employees FROM bob; missing ON keyword and wrong order.

3. Final Answer:

   The order of keywords is incorrect. -> Option A

4. Quick Check:

   REVOKE + privileges + ON + object + FROM + user [OK]

Hint: REVOKE syntax requires ON before object [OK]

Common Mistakes:

• Omitting ON keyword
• Swapping user and object positions
• Using ALL PRIVILEGES incorrectly

5. You want to allow user carol to insert and update data on table orders, but not delete. Which commands correctly grant these permissions?

hard

A. GRANT DELETE ON orders TO carol;

B. GRANT INSERT, UPDATE ON orders TO carol;

C. GRANT ALL PRIVILEGES ON orders TO carol;

D. GRANT SELECT, DELETE ON orders TO carol;

Solution

1. Step 1: Identify required permissions

   Carol needs INSERT and UPDATE permissions only, no DELETE.

2. Step 2: Match commands with required permissions

   GRANT INSERT, UPDATE ON orders TO carol; grants INSERT and UPDATE correctly. Options B and D grant DELETE, which is not wanted. GRANT ALL PRIVILEGES ON orders TO carol; grants all permissions, including DELETE.

3. Final Answer:

   GRANT INSERT, UPDATE ON orders TO carol; -> Option B

4. Quick Check:

   Grant only needed permissions, avoid ALL PRIVILEGES if not required [OK]

Hint: Grant only needed permissions, avoid ALL PRIVILEGES if unsure [OK]

Common Mistakes:

• Granting DELETE when not needed
• Using ALL PRIVILEGES carelessly
• Confusing SELECT with UPDATE