2. (2 points) Please find the dates without any placed order between the time range. (Hint: write a recursive query to create date sequence and use the select statement in Q1 to assign user-defined variables so that you can have a neat recursive query.)
时间: 2024-02-07 21:03:28 浏览: 25
Assuming that the table containing placed orders is called `orders` and has a column `order_date` of type DATE, the recursive query to generate a sequence of dates within a time range and then find the dates without any placed order would look like this:
```
WITH RECURSIVE dates(dt) AS (
SELECT start_date FROM (SELECT DATE('2022-01-01') AS start_date) vars
UNION ALL
SELECT dt + INTERVAL 1 DAY FROM dates WHERE dt < '2022-12-31'
)
SELECT dt FROM dates
WHERE dt NOT IN (
SELECT DISTINCT DATE(order_date) FROM orders
WHERE order_date BETWEEN '2022-01-01' AND '2022-12-31'
)
ORDER BY dt;
```
In this query, the recursive CTE `dates` generates a sequence of dates starting from January 1st, 2022 and ending on December 31st, 2022. The main query then selects all dates from this sequence that are not present in the `orders` table within the specified time range. The `DISTINCT` keyword is used to remove any duplicate dates from the `orders` table, and the `DATE()` function is applied to the `order_date` column to extract only the date part. Finally, the result is ordered by date in ascending order.