Column-level permissions in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to grant SELECT permission on the column 'email' of the 'users' table to user 'alice'.

PostgreSQL

GRANT SELECT ([1]) ON users TO alice;

Drag options to blanks, or click blank then click option'

Aid

Bpassword

Cemail

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Granting permission on the whole table instead of a specific column.

Using the wrong column name.

The GRANT SELECT (email) statement gives user 'alice' permission to read only the 'email' column in the 'users' table.

2fill in blank

medium

Complete the code to revoke SELECT permission on the 'salary' column from user 'bob'.

PostgreSQL

REVOKE SELECT ([1]) ON employees FROM bob;

Drag options to blanks, or click blank then click option'

Asalary

Bposition

Cdepartment

Dhire_date

Attempts:

3 left

💡 Hint

Common Mistakes

Revoking permission on the wrong column.

Forgetting to specify the column in parentheses.

The REVOKE SELECT (salary) statement removes the permission for user 'bob' to read the 'salary' column in the 'employees' table.

3fill in blank

hard

Fix the error in the code to grant SELECT permission on the 'phone' column to user 'carol'.

PostgreSQL

GRANT SELECT [1] ON contacts TO carol;

Drag options to blanks, or click blank then click option'

A( )

B(phone)

CON

Dphone

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses around the column name.

Adding extra keywords inside the parentheses.

The correct syntax requires parentheses around the column name: GRANT SELECT (phone) ON contacts TO carol;

4fill in blank

hard

Fill both blanks to grant SELECT permission on columns 'name' and 'email' to user 'dave'.

PostgreSQL

GRANT SELECT ([1], [2]) ON customers TO dave;

Drag options to blanks, or click blank then click option'

Aname

Bphone

Cemail

Daddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong column names.

Forgetting the comma between columns.

The statement grants SELECT permission on the 'name' and 'email' columns to user 'dave'.

5fill in blank

hard

Fill all three blanks to revoke SELECT permission on columns 'price', 'quantity', and 'discount' from user 'eve'.

PostgreSQL

REVOKE SELECT ([1], [2], [3]) ON sales FROM eve;

Drag options to blanks, or click blank then click option'

Aprice

Bquantity

Cdiscount

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Including columns not intended for revocation.

Missing commas between column names.

This revokes SELECT permission on the 'price', 'quantity', and 'discount' columns from user 'eve'.

Practice

1. What does column-level permission in PostgreSQL control?

easy

A. Access to server configuration files

B. Access to entire tables only

C. Access to database schemas

D. Access to specific columns in a table

Solution

1. Step 1: Understand the concept of column-level permissions

   Column-level permissions allow control over which columns a user can see or modify in a table.

2. Step 2: Compare with other access types

   Other options refer to broader or unrelated access controls, not specific columns.

3. Final Answer:

   Access to specific columns in a table -> Option D

4. Quick Check:

   Column-level permission = Access to specific columns [OK]

Hint: Column-level means controlling access per column, not whole table [OK]

Common Mistakes:

• Confusing column-level with table-level permissions
• Thinking it controls schema or server access
• Assuming it controls row-level access

2. Which of the following is the correct syntax to grant SELECT permission on column email of table users to user alice?

easy

A. GRANT SELECT(email) ON users TO alice;

B. GRANT SELECT ON users TO alice(email);

C. GRANT SELECT ON users(email) TO alice;

D. GRANT SELECT TO alice ON users(email);

Solution

1. Step 1: Recall PostgreSQL syntax for column-level GRANT

   The correct syntax is GRANT SELECT (email) ON users TO alice; (parentheses after privilege).

2. Step 2: Match options with syntax

   GRANT SELECT(email) ON users TO alice; matches the correct syntax exactly, others misplace keywords or parentheses.

3. Final Answer:

   GRANT SELECT(email) ON users TO alice; -> Option A

4. Quick Check:

   GRANT SELECT(column) ON table TO user [OK]

Hint: GRANT SELECT(column) ON table TO user is correct syntax [OK]

Common Mistakes:

• Placing column name after TO user
• Putting column inside ON table()
• Misordering keywords in the statement

3. Given the table employees(id, name, salary), if user bob has SELECT permission only on id and name, what will be the result of SELECT * FROM employees; executed by bob?

medium

A. Only id and name columns with data, salary as NULL

B. All columns with actual data

C. Error: permission denied

D. Only salary column with data

Solution

1. Step 1: Understand column-level permission effect on SELECT *

   User can see columns they have permission for; restricted columns appear as NULL.

2. Step 2: Apply to given columns

   Bob has permission on id and name, so salary shows as NULL.

3. Final Answer:

   Only id and name columns with data, salary as NULL -> Option A

4. Quick Check:

   Restricted columns show NULL, not error [OK]

Hint: Restricted columns appear as NULL, not error [OK]

Common Mistakes:

• Expecting a permission denied error
• Assuming all columns show data
• Thinking restricted columns are hidden completely

4. You run the command GRANT SELECT ON employees(name, salary) TO carol; but get a syntax error. What is the likely cause?

medium

A. Column names must be in double quotes

B. Cannot grant permissions on multiple columns at once

C. Column list in parentheses must precede the table name

D. User carol does not exist

Solution

1. Step 1: Check syntax for GRANT with multiple columns

   Correct syntax is GRANT SELECT (name, salary) ON employees TO carol;

2. Step 2: Identify error in command

   Command incorrectly places column list after table name; column list must follow SELECT before ON.

3. Final Answer:

   Column list in parentheses must precede the table name -> Option C

4. Quick Check:

   GRANT SELECT (col1, col2) ON table TO user [OK]

Hint: Columns inside parentheses after SELECT before ON table [OK]

Common Mistakes:

• Placing column list after table name
• Forgetting parentheses around columns
• Assuming multiple columns need separate GRANTs

5. You want to allow user dave to update only the phone column in the contacts table but not others. Which sequence of commands correctly achieves this?

hard

A. GRANT UPDATE(phone) ON contacts TO dave; REVOKE UPDATE ON contacts FROM dave;

B. REVOKE UPDATE ON contacts FROM dave; GRANT UPDATE(phone) ON contacts TO dave;

C. GRANT UPDATE ON contacts TO dave; REVOKE UPDATE(phone) ON contacts FROM dave;

D. GRANT UPDATE(phone) ON contacts TO dave;

Solution

1. Step 1: Remove any existing full UPDATE permission

   First revoke any broad UPDATE permission to avoid conflicts.

2. Step 2: Grant UPDATE permission only on the phone column

   Then grant UPDATE on the specific column to limit access.

3. Final Answer:

   REVOKE UPDATE ON contacts FROM dave; GRANT UPDATE(phone) ON contacts TO dave; -> Option B

4. Quick Check:

   Revoke broad then grant column-level UPDATE [OK]

Hint: Revoke broad permission before granting column-level update [OK]

Common Mistakes:

• Granting column-level without revoking broad permission
• Revoking column-level instead of broad permission
• Assuming single GRANT is enough if broad permission exists