选择每个人

Question

的最后一个记录，我有以下表

tbl_investors

id | first_name | last_name | 
--------------------------------------- 
    1 |  Jon  | Cold  | 
    2 |  Rob  | Ark  | 
    3 |  Rickon | Bolt  | 

tbl_investors_ledger

id | investor_id | amount | 
------------------------------------ 
    1 |  1  | 500 | 
    2 |  2  | 200 | 
    3 |  2  | 250 | 
    4 |  2  | 300 | 
    5 |  3  | 10  | 
    6 |  1  | 550 | 
    7 |  3  | 20  | 

我只是想向所有投资者与他们的最新量恢复。例如，Jon Cold与550，Rob Ark 300和Rickon Bolt 20，他们的姓氏按字母顺序排列。

我有一个现有的查询，但它不会返回最新的投资者数量。有人能帮助我，我做错了什么？

SELECT t1.*, t2.* 
    FROM ".tbl_investors." t1 
    LEFT JOIN ".tbl_investors_ledger." t2 
     ON t1.id = t2.investor_id 
    LEFT JOIN (SELECT t.investor_id, max(t.id) as tid 
     FROM ".tbl_investors_ledger." t) tt 
     ON tt.investor_id = t2.investor_id AND tt.tid = t2.id 
    GROUP BY t2.investor_id 
    ORDER BY t1.last_name 

Answer 1

试试这个;）

SELECT t1.*, t2.* 
FROM tbl_investors t1 
LEFT JOIN tbl_investors_ledger t2 
ON t1.id = t2.investor_id 
INNER JOIN (
    SELECT t.investor_id, max(t.id) as tid 
    FROM tbl_investors_ledger t GROUP BY t.investor_id) tt 
ON tt.investor_id = t2.investor_id AND tt.tid = t2.id 
ORDER BY t1.last_name 

SQLFiddle DEMO

并检查相关OP Retrieving the last record in each group和这个博客How to select the first/least/max row per group in SQL，你可以找到你的问题更多的解决方案。

Answer 2

您可以使用GROUP_CONCAT和SUBSTRING_INDEX一起

SELECT I.* 
    , SUBSTRING_INDEX(GROUP_CONCAT(L.amount ORDER BY L.id DESC), ',', 1) AS LastAmount 
    FROM tbl_investors AS I 
    LEFT JOIN tbl_investors_ledgers AS L 
     ON L.investor_id = I.id 
    GROUP BY I.id 
    ORDER BY I.last_name 

这里演示从SQLFiddle，非常感谢@zakhefron :)