Schema-level access control in PostgreSQL

Introduction

Schema-level access control helps you decide who can see or change groups of database objects. It keeps your data safe and organized.

You want to let only certain users see or change tables in a specific schema.

You have different teams working on different parts of the database and want to keep their data separate.

You want to prevent accidental changes by limiting who can add or remove tables in a schema.

You want to organize your database objects and control access by grouping them in schemas.

You want to give read-only access to some users for all objects in a schema.

Syntax

PostgreSQL

GRANT { { USAGE | CREATE } [, ...] | ALL [ PRIVILEGES ] } ON SCHEMA schema_name TO role_name;

REVOKE { { USAGE | CREATE } [, ...] | ALL [ PRIVILEGES ] } ON SCHEMA schema_name FROM role_name;

USAGE lets a user access objects in the schema (like tables).

CREATE lets a user add new objects (like tables) to the schema.

Examples

Allow user 'alice' to access objects in the 'sales' schema.

PostgreSQL

GRANT USAGE ON SCHEMA sales TO alice;

Allow user 'bob' to create new tables or objects in the 'marketing' schema.

PostgreSQL

GRANT CREATE ON SCHEMA marketing TO bob;

Remove access for 'alice' to use objects in the 'sales' schema.

PostgreSQL

REVOKE USAGE ON SCHEMA sales FROM alice;

Give all schema-level rights to the role 'hr_team' on the 'hr' schema.

PostgreSQL

GRANT ALL PRIVILEGES ON SCHEMA hr TO hr_team;

Sample Program

This example creates a schema named 'project' and a role named 'developer'. It then gives the developer role permission to use and create objects in the 'project' schema. Finally, it shows the granted privileges.

PostgreSQL

CREATE SCHEMA project;
CREATE ROLE developer;
GRANT USAGE ON SCHEMA project TO developer;
GRANT CREATE ON SCHEMA project TO developer;
-- Check privileges
SELECT grantee, privilege_type FROM information_schema.schema_privileges WHERE schema_name = 'project' AND grantee = 'developer';

Important Notes

Granting USAGE alone does not allow creating or modifying objects, only accessing them.

CREATE privilege is needed to add new tables or other objects inside the schema.

Always check current privileges with information_schema.schema_privileges to confirm access rights.

Summary

Schema-level access control manages who can use or add objects in a schema.

Use GRANT and REVOKE with USAGE and CREATE privileges to control access.

Check privileges anytime to keep your database secure and organized.

Practice

1. What does the USAGE privilege on a schema in PostgreSQL allow a user to do?

easy

A. Access objects within the schema without creating new ones

B. Create new tables and objects inside the schema

C. Delete the schema entirely

D. Modify data in tables outside the schema

Solution

1. Step 1: Understand USAGE privilege meaning

   The USAGE privilege allows a user to access objects inside the schema, such as selecting data from tables, but does not allow creating new objects.

2. Step 2: Differentiate from CREATE privilege

   The CREATE privilege is needed to add new tables or other objects. USAGE alone does not grant this ability.

3. Final Answer:

   Access objects within the schema without creating new ones -> Option A

4. Quick Check:

   USAGE = access only [OK]

Hint: USAGE lets you use, CREATE lets you add [OK]

Common Mistakes:

• Confusing USAGE with CREATE privilege
• Thinking USAGE allows schema deletion
• Assuming USAGE grants data modification outside schema

2. Which of the following is the correct syntax to grant CREATE privilege on a schema named sales to user alice?

easy

A. GRANT CREATE ON sales TO alice;

B. GRANT CREATE TO alice ON SCHEMA sales;

C. GRANT CREATE ON SCHEMA sales TO alice;

D. GRANT CREATE ON DATABASE sales TO alice;

Solution

1. Step 1: Identify correct GRANT syntax for schema

   In PostgreSQL, to grant privileges on a schema, the syntax is: GRANT privilege ON SCHEMA schema_name TO user;

2. Step 2: Match syntax with options

   GRANT CREATE ON SCHEMA sales TO alice; matches this syntax exactly: GRANT CREATE ON SCHEMA sales TO alice;

3. Final Answer:

   GRANT CREATE ON SCHEMA sales TO alice; -> Option C

4. Quick Check:

   GRANT ... ON SCHEMA ... TO ... [OK]

Hint: Use 'ON SCHEMA' when granting schema privileges [OK]

Common Mistakes:

• Omitting 'SCHEMA' keyword
• Using 'ON DATABASE' instead of 'ON SCHEMA'
• Placing TO clause incorrectly

3. Given the commands below, what will be the result of SELECT * FROM sales.orders; when run by user bob?

GRANT USAGE ON SCHEMA sales TO bob;
REVOKE CREATE ON SCHEMA sales FROM bob;

medium

A. Query runs but returns no rows

B. Error: permission denied for schema sales

C. Error: relation sales.orders does not exist

D. Query runs successfully and returns rows from sales.orders

Solution

1. Step 1: Analyze granted privileges

   User bob has USAGE on schema sales, so can access objects inside it. CREATE privilege is revoked, so bob cannot create new objects but can read existing ones.

2. Step 2: Understand effect on SELECT query

   Since bob has USAGE, SELECT on sales.orders will work if bob has SELECT privilege on the table (assumed). The REVOKE of CREATE does not affect SELECT.

3. Final Answer:

   Query runs successfully and returns rows from sales.orders -> Option D

4. Quick Check:

   USAGE allows access, REVOKE CREATE blocks creation only [OK]

Hint: USAGE lets you read; CREATE controls adding objects [OK]

Common Mistakes:

• Confusing CREATE with SELECT privilege
• Assuming REVOKE CREATE blocks all access
• Ignoring USAGE privilege effect

4. You want to allow user carol to create tables in schema inventory, but she gets an error: permission denied for schema inventory. Which command fixes this?

medium

A. GRANT CREATE ON SCHEMA inventory TO carol;

B. GRANT USAGE ON SCHEMA inventory TO carol;

C. GRANT ALL PRIVILEGES ON SCHEMA inventory TO carol;

D. REVOKE USAGE ON SCHEMA inventory FROM carol;

Solution

1. Step 1: Understand error cause

   To create tables, user needs both USAGE and CREATE privileges on the schema. Without USAGE, permission denied error occurs.

2. Step 2: Grant missing privilege

   Granting USAGE on schema inventory to carol allows her to access the schema and create tables if CREATE is already granted.

3. Final Answer:

   GRANT USAGE ON SCHEMA inventory TO carol; -> Option B

4. Quick Check:

   USAGE needed before CREATE works [OK]

Hint: Grant USAGE before CREATE to avoid permission errors [OK]

Common Mistakes:

• Granting CREATE without USAGE privilege
• Revoking instead of granting privileges
• Assuming ALL PRIVILEGES always needed

5. You want to restrict user dave so he can only create objects in schema projects but cannot access any existing objects. Which combination of privileges achieves this?

hard

A. GRANT CREATE ON SCHEMA projects TO dave; REVOKE USAGE ON SCHEMA projects FROM dave;

B. GRANT USAGE ON SCHEMA projects TO dave; REVOKE CREATE ON SCHEMA projects FROM dave;

C. GRANT ALL ON SCHEMA projects TO dave;

D. REVOKE ALL ON SCHEMA projects FROM dave;

Solution

1. Step 1: Understand privilege effects

   CREATE allows adding new objects. USAGE allows accessing existing objects. To restrict access but allow creation, grant CREATE and revoke USAGE.

2. Step 2: Apply correct commands

   GRANT CREATE ON SCHEMA projects TO dave; REVOKE USAGE ON SCHEMA projects FROM dave; grants CREATE and revokes USAGE, so dave can create but not access existing objects.

3. Final Answer:

   GRANT CREATE ON SCHEMA projects TO dave; REVOKE USAGE ON SCHEMA projects FROM dave; -> Option A

4. Quick Check:

   Create without usage blocks access [OK]

Hint: Grant CREATE, revoke USAGE to allow creation only [OK]

Common Mistakes:

• Granting USAGE allows access to existing objects
• Revoking CREATE disables creation
• Granting ALL gives too many rights