Permissions in relational databases are managed through a combination of SQL commands, role-based access control, and object-level privileges. Most systems, like PostgreSQL, MySQL, or SQL Server, use a structured approach where permissions are explicitly granted or revoked on database objects (tables, views, procedures) to users or roles. The core mechanism involves the GRANT and REVOKE SQL statements, which define what actions a user or role can perform. For example, GRANT SELECT ON employees TO analyst_role; allows anyone assigned to analyst_role to read the employees table. Permissions are hierarchical: a user might inherit privileges through roles, and administrators can manage access at granular levels, such as columns or rows in some systems.
A typical workflow involves creating roles (e.g., read_only, data_editor) and assigning specific privileges to them. For instance, a read_only role might have SELECT permissions on all tables, while a data_editor role could have INSERT, UPDATE, and DELETE access. Users are then assigned one or more roles, streamlining permission management. For example, a developer might grant EXECUTE on a stored procedure to an api_user account but restrict direct table access. Some databases also support schema-level permissions—like granting USAGE on a schema to allow access to all objects within it. This reduces the need to manage permissions for each table individually.
Advanced features include row-level security (e.g., PostgreSQL’s policies) or column-level restrictions. For example, a policy could limit access to rows where department_id matches the user’s department. Ownership also plays a role: the creator of a database object automatically has full privileges and can grant permissions to others. Security best practices, like the principle of least privilege, are enforced by granting only necessary permissions. Auditing tools or system tables (e.g., information_schema.table_privileges) help track existing permissions. For instance, querying SELECT * FROM information_schema.table_privileges WHERE grantee = 'user123'; shows what tables user123 can access. This structured yet flexible system ensures precise control over data access.