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                         使用以下MySQL表包含带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?我已经尝试将表加入到自身中以计算所有借方和贷方总计,但有些东西无法正常工作. 
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;
 
我期待的结果是: 
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.任何帮助都会很棒.
最佳答案
 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),500),(2,1200),(3,(4,1000);
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,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 |
+-----------+--------------+---------------+---------+
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