Find the department with the highest average salary using a derived table.

Problem Statement

<p>Find the department with the highest average salary using a derived table.</p>

Examples

Input: employees table: +----+---------+------------+--------+ | id | name | department | salary | +----+---------+------------+--------+ | 1 | Alice | IT | 90000 | | 2 | Bob | HR | 60000 | | 3 | Charlie | IT | 120000 | | 4 | Dana | HR | 75000 | +----+---------+------------+--------+

Output: +------------+---------------------+ | department | avg_sal | +------------+---------------------+ | IT | 105000.000000000000 | +------------+---------------------+

Explanation: The query retrieves the requested records satisfying all problem requirements.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Identify the grouping dimension(s) and which columns require aggregate functions (such as COUNT, SUM, AVG, MIN, or MAX). 💡 Hint 2: Add the GROUP BY clause for all non-aggregated columns listed in the SELECT projection. 💡 Hint 3: If filtering groups, use HAVING; otherwise use WHERE before grouping: SELECT <group_col>, <AGG>(...) FROM <table> GROUP BY <group_col>;

Editorial & Approach

Problem Overview & Intuition

To solve "Subquery in FROM (Derived Table)", we query the relational database engine using declarative SQL. The goal is to find the department with the highest average salary using a derived table. By formulating an optimal execution plan with appropriate projection and filtering, the database engine executes the query with minimal overhead.

Step-by-Step Approach

Analyze Schema: Identify the target tables, necessary foreign keys, and expected output columns.
Construct Filtering & Logic: Apply grouping & aggregates to isolate the requested data.
Format & Order: Sort the resulting records according to specified order criteria.

Optimal Implementation (SQL)

SELECT department, avg_sal FROM (SELECT department, AVG(salary) AS avg_sal FROM employees GROUP BY department) sub ORDER BY avg_sal DESC LIMIT 1;

Complexity Analysis

Time Complexity O(N log N) for sorting or partitioning rows.

Space Complexity O(N) for intermediate group hash tables or window buffers.

Key Considerations & Edge Cases

Empty Tables: The query executes safely returning zero rows without syntax error.
NULL Values: Columns containing NULL values are properly handled by standard ANSI SQL semantics.
Case Sensitivity: String comparisons and keywords adhere to PostgreSQL/standard SQL rules.

Subquery in FROM (Derived Table)

Medium

Find the department with the highest average salary using a derived table.

Example Scenarios

1Example 1

Input:

employees table

id	name	department	salary
1	Alice	IT	90000
2	Bob	HR	60000
3	Charlie	IT	120000
4	Dana	HR	75000

Output:

department	avg_sal
IT	105000.000000000000

Explanation:

The query retrieves the requested records satisfying all problem requirements.

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