Analyzing Query Performance

Problem

Your complex JOIN is taking 3 minutes to run, and you have no idea why. A DBA suggests you ask the database how it plans to execute the query before it actually runs it. Prefix this query with EXPLAIN to view its execution plan: SELECT * FROM employees WHERE salary > 100000;.

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.

Try It

Hint

Solution