Substituting NULLs with COALESCE

Problem

In the employee structure, top-level managers do not have a manager ID. For a clean organization report, substitute any NULL value in the manager_id column with 0. Output first_name, last_name, and the cleaned manager ID as clean_manager_id.

Database Schema

Table: employees

• employee_id (INT): Unique identifier for the employee.
• first_name (VARCHAR): First name of the employee.
• last_name (VARCHAR): Last name of the employee.
• salary (INT): Employee's salary.
• department_id (INT): Foreign key referencing the department.
• manager_id (INT): Foreign key referencing the manager (another employee).
• hire_date (DATE): Date the employee was hired.

Table: departments

• department_id (INT): Unique identifier for the department.
• department_name (VARCHAR): Name of the department.

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Hint

Solution