左连接 - Select ALL 来自左表，但 select 仅来自右表的最新

Question

我有 2 张桌子，借款人和贷款。 我想在主页上显示所有有或没有贷款的借款人的列表。 如果有贷款，显示最新的。

我有以下 sql 查询，基本上它返回上述描述，除了它显示借款人的第一笔贷款而不是最新贷款。

（旁注：我使用 GROUP BY 来避免重复。没有它，如果有多个贷款，查询会返回重复的借款人姓名。只是想知道这是否是一种有效的方法。）

SELECT b.b_id, 
       b.isdeleted, 
       b.picture, 
       b.firstname, 
       b.middlename, 
       b.lastname, 
       b.address, 
       b.contactno,
       b.birthday, 
       b.businessname, 
       b.occupation, 
       b.comaker, 
       b.comakerno, 
       b.remarks, 
       b.datecreated, 
       b.activeloan,
       l.l_id, 
       l.amount, 
       l.payable, 
       l.balance, 
       l.mode, 
       l.term, 
       l.interestrate, 
       l.amortization,
       l.releasedate, 
       l.duedate, 
       l.status, 
       l.c_id
FROM borrowers as b
LEFT JOIN loans as l ON b.b_id = l.b_id
WHERE b.isdeleted = 0
GROUP BY b.b_id

Answer 1

看来下面的查询正是我想要的。

我在“ON”子句中添加了以下子查询。

(SELECT MAX(l_id)
 FROM jai_db.loans as l2
 WHERE l2.b_id = b.b_id LIMIT 1)

SELECT b.b_id, b.isdeleted, b.picture, b.firstname, b.middlename, b.lastname, b.address, b.contactno,
                                    b.birthday, b.businessname, b.occupation, b.comaker, b.comakerno, b.remarks, b.datecreated, b.activeloan,
                                    l.l_id, l.amount, l.payable, l.balance, l.mode, l.term, l.interestrate, l.amortization,
                                    l.releasedate, l.duedate, l.status, l.c_id
                             FROM jai_db.borrowers as b
                             LEFT JOIN jai_db.loans as l
                             ON l.l_id = (SELECT MAX(l_id)
                                          FROM jai_db.loans as l2
                                          WHERE l2.b_id = b.b_id LIMIT 1) 
                             WHERE b.isdeleted = 0