LeetCode：Database 65.每月交易 I

Posted 2021-06-26 Xiao Miao

要求：编写一个 sql 查询来查找每个月和每个国家/地区的事务数及其总金额、已批准的事务数及其总金额。

Transactions 表的结构：

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| country       | varchar |
| state         | enum    |
| amount        | int     |
| trans_date    | date    |
+---------------+---------+
id 是这个表的主键。
该表包含有关传入事务的信息。
state 列类型为 “[”批准“，”拒绝“] 之一。

Transactions 表:

+------+---------+----------+--------+------------+
| id   | country | state    | amount | trans_date |
+------+---------+----------+--------+------------+
| 121  | US      | approved | 1000   | 2018-12-18 |
| 122  | US      | declined | 2000   | 2018-12-19 |
| 123  | US      | approved | 2000   | 2019-01-01 |
| 124  | DE      | approved | 2000   | 2019-01-07 |
+------+---------+----------+--------+------------+

Result Table:

+----------+---------+-------------+----------------+--------------------+-----------------------+
| month    | country | trans_count | approved_count | trans_total_amount | approved_total_amount |
+----------+---------+-------------+----------------+--------------------+-----------------------+
| 2018-12  | US      | 2           | 1              | 3000               | 1000                  |
| 2019-01  | US      | 1           | 1              | 2000               | 2000                  |
| 2019-01  | DE      | 1           | 1              | 2000               | 2000                  |
+----------+---------+-------------+----------------+--------------------+-----------------------+

SQL语法：

SELECT d1 AS month,c1 AS country,COUNT(i1) AS trans_count,
COUNT(i2) AS approved_count,SUM(a1) AS trans_total_amount,
ifnull(SUM(a2),0) AS approved_total_amount
FROM(
SELECT SUBSTR(a.trans_date,1,7) AS d1,a.country AS c1,a.id AS i1,b.id AS i2,a.amount AS a1,b.amount AS a2
FROM
Transactions a
LEFT JOIN Transactions b
ON a.id=b.id
AND b.state='approved')c
GROUP BY d1,c1;