bank-account-summary-ii.sql

/*

Description
LeetCode Problem 1587.

Table: Users

+--------------+---------+
| Column Name  | Type    |
+--------------+---------+
| account      | int     |
| name         | varchar |
+--------------+---------+
account is the primary key for this table.
Each row of this table contains the account number of each user in the bank.
Table: Transactions

+---------------+---------+
| Column Name   | Type    |
+---------------+---------+
| trans_id      | int     |
| account       | int     |
| amount        | int     |
| transacted_on | date    |
+---------------+---------+
trans_id is the primary key for this table.
Each row of this table contains all changes made to all accounts.
amount is positive if the user received money and negative if they transferred money.
All accounts start with a balance 0.
Write an SQL query to report the name and balance of users with a balance higher than 10000. The balance of an account is equal to the sum of the amounts of all transactions involving that account.

Return the result table in any order.

The query result format is in the following example.

Users table:
+------------+--------------+
| account    | name         |
+------------+--------------+
| 900001     | Alice        |
| 900002     | Bob          |
| 900003     | Charlie      |
+------------+--------------+

Transactions table:
+------------+------------+------------+---------------+
| trans_id   | account    | amount     | transacted_on |
+------------+------------+------------+---------------+
| 1          | 900001     | 7000       |  2020-08-01   |
| 2          | 900001     | 7000       |  2020-09-01   |
| 3          | 900001     | -3000      |  2020-09-02   |
| 4          | 900002     | 1000       |  2020-09-12   |
| 5          | 900003     | 6000       |  2020-08-07   |
| 6          | 900003     | 6000       |  2020-09-07   |
| 7          | 900003     | -4000      |  2020-09-11   |
+------------+------------+------------+---------------+

Result table:
+------------+------------+
| name       | balance    |
+------------+------------+
| Alice      | 11000      |
+------------+------------+
Alice's balance is (7000 + 7000 - 3000) = 11000.
Bob's balance is 1000.
Charlie's balance is (6000 + 6000 - 4000) = 8000.

*/

# V0
SELECT u.name,
       SUM(amount) balance
FROM users u
INNER JOIN transactions t ON u.account = t.account
GROUP BY u.name
HAVING balance > 10000
ORDER BY NULL;

# V1
# https://circlecoder.com/bank-account-summary-II/
select name, balance
from (select account, sum(amount) as balance
    from Transactions
    group by account
    having sum(amount) > 10000) t
join Users u
on u.account = t.account;

# V2
# Time:  O(m + n)
# Space: O(m + n)
SELECT u.name,
       SUM(amount) balance
FROM users u
INNER JOIN transactions t ON u.account = t.account
GROUP BY u.name
HAVING balance > 10000
ORDER BY NULL;