1193. Monthly Transactions I

Description of Problem

Table: Transactions

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| id            | int     |
| country       | varchar |
| state         | enum    |
| amount        | int     |
| trans_date    | date    |
+---------------+---------+
id is the primary key of this table.
The table has information about incoming transactions.
The state column is an enum of type ["approved", "declined"].

Write an SQL query to find for each month and country, the number of transactions and their total amount, the number of approved transactions and their total amount.

Return the result table in any order.

The query result format is in the following example.

Example 1:

Input: 
Transactions table:
+------+---------+----------+--------+------------+
| 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 |
+------+---------+----------+--------+------------+
Output: 
+----------+---------+-------------+----------------+--------------------+-----------------------+
| 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                  |
+----------+---------+-------------+----------------+--------------------+-----------------------+

Solution

Tags: SQL Aggregate Functions Grouping

Explanation

Hints: Make month a new column and use GROUP BY.

Code (MySQL)

SELECT 
    CONCAT(YEAR(trans_date),'-',LPAD(MONTH(trans_date),2,'0')) AS month, 
    country, 
    COUNT(1) AS trans_count, 
    SUM(state = 'approved') AS approved_count, 
    SUM(amount) AS trans_total_amount, 
    SUM(IF(state = 'approved', amount,0)) AS approved_total_amount
FROM Transactions
GROUP BY month, country;