Find employees who earn more than the average salary of their department.

Problem Statement

<p>Find <code>employees</code> who earn more than the average salary of their department.</p>

Examples

Input: employees table: +----+---------+------------+--------+ | id | name | department | salary | +----+---------+------------+--------+ | 1 | Alice | IT | 90000 | | 2 | Bob | IT | 60000 | | 3 | Charlie | IT | 120000 | | 4 | Dana | HR | 50000 | | 5 | Eve | HR | 80000 | +----+---------+------------+--------+

Output: +---------+------------+--------+ | name | department | salary | +---------+------------+--------+ | Charlie | IT | 120000 | | Eve | HR | 80000 | +---------+------------+--------+

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

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Identify the filtering conditions needed to isolate the target rows from the table. 💡 Hint 2: Use appropriate operators: = for exact matches, LIKE for wildcard patterns, IN for sets, or BETWEEN for numeric/date ranges. 💡 Hint 3: Combine filters with AND/OR if multiple conditions exist: SELECT <cols> FROM <table> WHERE <condition>;

Editorial & Approach

Problem Overview & Intuition

To solve "Correlated Subquery", we query the relational database engine using declarative SQL. The goal is to find employees who earn more than the average salary of their department. 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 WHERE filtering to isolate the requested data.
Format & Order: Ensure columns match the expected project schema in order.

Optimal Implementation (SQL)

SELECT name, department, salary FROM employees e WHERE salary > (SELECT AVG(salary) FROM employees e2 WHERE e2.department = e.department);

Complexity Analysis

Time Complexity O(N) full table scan or O(log N) if filtered column is indexed.

Space Complexity O(K) where K is the number of filtered rows returned.

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.

Correlated Subquery

Medium

Find employees who earn more than the average salary of their department.

Example Scenarios

1Example 1

Input:

employees table

id	name	department	salary
1	Alice	IT	90000
2	Bob	IT	60000
3	Charlie	IT	120000
4	Dana	HR	50000
5	Eve	HR	80000

Output:

name	department	salary
Charlie	IT	120000
Eve	HR	80000

Explanation:

The query retrieves the requested records satisfying all problem requirements.

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