php - 从两个表中选择所有行，从最后一个表mysql中选择一行

Question

我想从两个表中选择所有行，从最后一个表中选择一行

我的表格如下，

tbl_order

order_id    order_no
--------    --------
   1         1000
   2         1001
   3         1002

tbl_assign

assign_id    order_id    central_status
---------    --------    --------------
    1           1              1
    2           2              1
    3           3              1

tbl_unit_status

status_id    assign_id    status_status
---------    ---------    -------------
    1            1             Work
    2            2             Cutter
    3            2             Stitch
    4            1             Stitch

从上面的 3 个表中，我想要的结果是，

order_id    order_no    assign_id    status_status
--------    --------    ---------    -------------
   3          1002          3           {null}
   2          1001          2           Stitch
   1          1000          1           Stitch

我试过下面的代码，

SELECT * FROM tbl_order o LEFT JOIN tbl_assign a ON a.order_id = o.order_id LEFT JOIN (SELECT * FROM tbl_unit_status u ORDER BY u.status_id DESC LIMIT 1) uu ON uu.assign_id = a.assign_id WHERE a.central_status = 1 ORDER BY a.assign_id DESC

但结果是，

order_id    order_no    assign_id    status_status
--------    --------    ---------    -------------
   3          1002          3           {null}
   2          1001          2           {null}
   1          1000          1           Stitch

哪里做错了。我已经尝试了很多。请帮我找到答案。谢谢。

Answer 1

像这样尝试:

SELECT o.*,u2.assign_id,u2.status_status FROM tbl_order o 
LEFT JOIN tbl_assign a ON a.order_id = o.order_id LEFT JOIN 
(SELECT u.assign_id,max(u.status_id) as maxid FROM tbl_unit_status u  group by u.assign_id) 
uu ON uu.assign_id = a.assign_id
LEFT JOIN tbl_unit_status  u2 on u2.status_id = uu.maxid
 WHERE a.central_status = 1 ORDER BY a.assign_id DESC