Use two CTEs: one for high earners (salary > 80000) and one for IT employees. Find the intersection.

Problem Statement

<p>Use two CTEs: one for high earners (salary > 80000) and one for IT <code>employees</code>. Find the intersection.</p>

Examples

Input: employees table: +----+---------+------------+--------+ | id | name | department | salary | +----+---------+------------+--------+ | 1 | Alice | IT | 90000 | | 2 | Bob | HR | 85000 | | 3 | Charlie | IT | 60000 | | 4 | Dana | IT | 120000 | +----+---------+------------+--------+

Output: +-------+--------+ | name | salary | +-------+--------+ | Alice | 90000 | | Dana | 120000 | +-------+--------+

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

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Determine which tables contain the required columns and relate them using INNER JOIN on the corresponding foreign/primary keys. 💡 Hint 2: Write out the ON condition matching key fields (e.g. ON a.key = b.key) and apply any filtering in the WHERE clause. 💡 Hint 3: Select only the requested columns in the SELECT clause with clear aliases if needed: SELECT ... FROM ... INNER JOIN ... ON ...;

Editorial & Approach

Problem Overview & Intuition

To solve "Multiple CTEs Combined", we query the relational database engine using declarative SQL. The goal is to use two ctes: one for high earners (salary > 80000) and one for it employees. find the intersection. 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 table joins to isolate the requested data.
Format & Order: Ensure columns match the expected project schema in order.

Optimal Implementation (SQL)

WITH high_earners AS (SELECT * FROM employees WHERE salary > 80000), it_employees AS (SELECT * FROM employees WHERE department = 'IT') SELECT h.name, h.salary FROM high_earners h INNER JOIN it_employees i ON h.id = i.id;

Complexity Analysis

Time Complexity O(N * M) worst-case, O(N + M) with hash/merge join on indexed keys.

Space Complexity O(N) for join buffer and result set.

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.

Multiple CTEs Combined

Hard

Use two CTEs: one for high earners (salary > 80000) and one for IT employees. Find the intersection.

Example Scenarios

1Example 1

Input:

employees table

id	name	department	salary
1	Alice	IT	90000
2	Bob	HR	85000
3	Charlie	IT	60000
4	Dana	IT	120000

Output:

name	salary
Alice	90000
Dana	120000

Explanation:

The query retrieves the requested records satisfying all problem requirements.

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