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2893. Calculate Orders Within Each Interval πŸ”’

DifficultyMedium

Description

Table: Orders

+-------------+------+ 
| Column Name | Type | 
+-------------+------+ 
| minute      | int  | 
| order_count | int  |
+-------------+------+
minute is the primary key for this table.
Each row of this table contains the minute and number of orders received during that specific minute. The total number of rows will be a multiple of 6.

Write a query to calculate total orders within each interval. Each interval is defined as a combination of 6 minutes.

  • Minutes 1 to 6 fall within interval 1, while minutes 7 to 12 belong to interval 2, and so forth.

Return the result table ordered by interval_no in ascending order.

The result format is in the following example.

 

Example 1:

Input: 
Orders table:
+--------+-------------+
| minute | order_count | 
+--------+-------------+
| 1      | 0           |
| 2      | 2           | 
| 3      | 4           | 
| 4      | 6           | 
| 5      | 1           | 
| 6      | 4           | 
| 7      | 1           | 
| 8      | 2           | 
| 9      | 4           | 
| 10     | 1           | 
| 11     | 4           | 
| 12     | 6           | 
+--------+-------------+
Output: 
+-------------+--------------+
| interval_no | total_orders | 
+-------------+--------------+
| 1           | 17           | 
| 2           | 18           |    
+-------------+--------------+
Explanation: 
- Interval number 1 comprises minutes from 1 to 6. The total orders in these six minutes are (0 + 2 + 4 + 6 + 1 + 4) = 17.
- Interval number 2 comprises minutes from 7 to 12. The total orders in these six minutes are (1 + 2 + 4 + 1 + 4 + 6) = 18.
Returning table orderd by interval_no in ascending order.

Solutions

Solution 1

Thinking

Each block of six minutes is one interval. A ROWS 5 PRECEDING running sum after ordering by minute, kept only when minute is a multiple of \(6\), reports the sum at each interval's right end.

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# Write your MySQL query statement below
WITH
    T AS (
        SELECT
            minute,
            SUM(order_count) OVER (
                ORDER BY minute
                ROWS 5 PRECEDING
            ) AS total_orders
        FROM Orders
    )
SELECT minute / 6 AS interval_no, total_orders
FROM T
WHERE minute % 6 = 0;

Solution 2

Thinking

The window still walks a prefix. When minutes are consecutive, \(\lfloor(minute+5)/6\rfloor\) groups rows directly and SUM inside each group is the interval total.

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SELECT
    FLOOR((minute + 5) / 6) AS interval_no,
    SUM(order_count) AS total_orders
FROM Orders
GROUP BY 1
ORDER BY 1;

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