使用MySQL在单个表中根据借方和贷方计算余额

Question

使用下面的MySQL表包含具有相关金额的借方或贷方“操作”，如何选择具有非零“余额”的所有CLIENT_ID？我尝试将表格与自身连接起来以计算所有借方和贷方总计，但某些方法无法正常工作。

CLIENT_ID    ACTION_TYPE    ACTION_AMOUNT
1            debit          1000
1            credit         100
1            credit         500
2            debit          1000
2            credit         1200
3            debit          1000
3            credit         1000
4            debit          1000

我的MySQL查询不起作用：

SELECT 
    client_id,
    SUM(t_debits) AS debits, 
    SUM(t_credits) AS credits, 
    SUM(t_debits)-SUM(t_credits) AS balance
FROM table_name AS t_debits
LEFT JOIN table_name AS t_credits ON t_credits.client_id=t_debits.client_id
WHERE 
    t_debits.action_type='debit'
    AND t_credits.action_type='credit'
    AND balance!=0
GROUP BY t_debits.client_id, t_credits.client_id;

我期望的结果是这样的：

CLIENT_ID    DEBITS    CREDITS    BALANCE
1            1000      600        400
2            1000      1200       -200
4            1000      0          1000

我不知道还有什么可以尝试的。任何帮助将是巨大的。

Answer 1

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table
(transaction_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,client_id INT NOT NULL
,action_type VARCHAR(12) NOT NULL
,action_amount INT NOT NULL
);

INSERT INTO my_table(client_id,action_type,action_amount) VALUES
(1            ,'debit',         1000),
(1            ,'credit',         100),
(1            ,'credit',         500),
(2            ,'debit',          1000),
(2            ,'credit',         1200),
(3            ,'debit',          1000),
(3            ,'credit',         1000),
(4            ,'debit',          1000);


SELECT client_id
     , SUM(COALESCE(CASE WHEN action_type = 'debit' THEN action_amount END,0)) total_debits
     , SUM(COALESCE(CASE WHEN action_type = 'credit' THEN action_amount END,0)) total_credits
     , SUM(COALESCE(CASE WHEN action_type = 'debit' THEN action_amount END,0)) 
     - SUM(COALESCE(CASE WHEN action_type = 'credit' THEN action_amount END,0)) balance 
  FROM my_table 
 GROUP  
    BY client_id
HAVING balance <> 0;


+-----------+--------------+---------------+---------+
| client_id | total_debits | total_credits | balance |
+-----------+--------------+---------------+---------+
|         1 |         1000 |           600 |     400 |
|         2 |         1000 |          1200 |    -200 |
|         4 |         1000 |             0 |    1000 |
+-----------+--------------+---------------+---------+