Assign a dense rank to products by price (descending). No gaps in ranking after ties.

Problem Statement

<p>Assign a dense rank to <code>products</code> by price (descending). No gaps in ranking after ties.</p>

Examples

Input: products table: +----+------+-------+ | id | name | price | +----+------+-------+ | 1 | A | 100 | | 2 | B | 200 | | 3 | C | 200 | | 4 | D | 150 | +----+------+-------+

Output: +------+-------+----+ | name | price | dr | +------+-------+----+ | B | 200 | 1 | | C | 200 | 1 | | D | 150 | 2 | | A | 100 | 3 | +------+-------+----+

Explanation: The window function evaluates the calculation across the partition in the specified ordering.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Use a window function with OVER (...) to compute values across rows related to the current row without collapsing them like GROUP BY. 💡 Hint 2: Check if PARTITION BY is required to split windows by category or if only an ORDER BY inside OVER (...) is needed. 💡 Hint 3: Structure the query as: <window_func>() OVER (PARTITION BY ... ORDER BY ...) AS <alias>;

Editorial & Approach

Problem Overview & Intuition

To solve "Window Function: DENSE_RANK", we query the relational database engine using declarative SQL. The goal is to assign a dense rank to products by price (descending). no gaps in ranking after ties. 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 row projections to isolate the requested data.
Format & Order: Sort the resulting records according to specified order criteria.

Optimal Implementation (SQL)

SELECT name, price, DENSE_RANK() OVER (ORDER BY price DESC) AS dr FROM products;

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.

Window Function: DENSE_RANK

Medium

Assign a dense rank to products by price (descending). No gaps in ranking after ties.

Example Scenarios

1Example 1

Input:

products table

id	name	price
1	A	100
2	B	200
3	C	200
4	D	150

Output:

name	price	dr
B	200	1
C	200	1
D	150	2
A	100	3

Explanation:

The window function evaluates the calculation across the partition in the specified ordering.

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