Calculate the running total of sales ordered by date.

Problem Statement

<p>Calculate the running total of <code>sales</code> ordered by date.</p>

Examples

Input: sales table: +------------+--------+ | sale_date | amount | +------------+--------+ | 2023-01-01 | 100 | | 2023-01-02 | 150 | | 2023-01-03 | 50 | +------------+--------+

Output: +--------------------------+--------+---------------+ | sale_date | amount | running_total | +--------------------------+--------+---------------+ | 2023-01-01T00:00:00.000Z | 100 | 100 | | 2023-01-02T00:00:00.000Z | 150 | 250 | | 2023-01-03T00:00:00.000Z | 50 | 300 | +--------------------------+--------+---------------+

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

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 "Calculate Running Total", we query the relational database engine using declarative SQL. The goal is to calculate the running total of sales ordered by date. 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 sale_date, amount, SUM(amount) OVER (ORDER BY sale_date) AS running_total FROM sales;

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.

Calculate Running Total

Medium

Calculate the running total of sales ordered by date.

Example Scenarios

1Example 1

Input:

sales table

sale_date	amount
2023-01-01	100
2023-01-02	150
2023-01-03	50

Output:

sale_date	amount	running_total
2023-01-01T00:00:00.000Z	100	100
2023-01-02T00:00:00.000Z	150	250
2023-01-03T00:00:00.000Z	50	300

Explanation:

The query retrieves the requested records satisfying all problem requirements.

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