問題描述

問題解答

select u2.username as borrower,u1.username as debtor,sum(b.amount) as debt from borrow_log b left join users u1 on b.debtor = u1.id left join users u2 on b.borrower = u2.id where u1.gender = 1 group by b.borrower,b.debtor;回答2：

SELECT (SELECT us.username FROM users us WHERE us.id=a.borrow) AS borrow_name, (SELECT us.username FROM users us WHERE us.id=a.debtor) AS debtor_name, SUM(amount) AS total_amount FROM borrow_log a LEFT JOIN users b ON a.debtor = b.id WHERE b.gender = 1 GROUP BY a.borrow,a.debtor回答3：

SELECT a1.*,a2.username AS debname,a3.username AS borrowname,SUM(a1.amount) FROM a1 LEFT JOIN a2 ON a1.debtor=a2.id LEFT JOIN a2 AS a3 ON a1.borrower=a3.id WHERE a2.gender=1 GROUP BY a1.debtor ,a1.borrower