如何基于两个不同的列选择行？

Question

我有这样的桌子

id  type        type_id cust    ip_address      datetime
395 Category    5       0       119.63.196.29   2012-11-27 00:34:21
394 Cart        812     0       84.208.217.178  2012-11-27 00:31:48
393 Cart        812     0       84.208.217.178  2012-11-27 00:31:41
392 Cart        812     0       84.208.217.178  2012-11-27 00:31:35
391 Product     812     0       84.208.217.178  2012-11-27 00:31:34

我想选择按ID desc排序的4行，它们具有不同的type + type_id数据。

因此查询的结果将删除id 393和392，因为type和type_id组合已经在id 394中。

伪代码：从类型和类型_结果与结果集不同的表中选择*，按ID desc限制4

Answer 1

select * from table
where id in 
(
  select min(id)
  from table 
  group by  type, type_id 
)
order by id desc
limit 4

Answer 2

SELECT *
  FROM AnonymousTable AS a1
  JOIN (SELECT type, type_id, MAX(id) AS id
          FROM AnonymousTable
         GROUP BY type, type_id
       ) AS a2
    ON a1.type = a2.type AND a1.type_id = a2.type_id AND a1.id = a2.id

但是，由于ID值可能是唯一的，因此您可以简化子查询和随后的联接：

SELECT *
  FROM AnonymousTable AS a1
  JOIN (SELECT MAX(id) AS id
          FROM AnonymousTable
         GROUP BY type, type_id
       ) AS a2
    ON a1.id = a2.id

即使id不是唯一的（只要id ， type和type_id的组合是唯一的），较长的格式也会产生正确的答案。

Answer 3

尝试这个：

SELECT t1.* 
FROM table t1
INNER JOIN 
(
   SELECT MAX(id) maxid, type_id, type
   FROM table
   GROUP BY type_id, type
) t2 ON t1.id = t2.maxid AND t1.type = t2.type AND t1.type_id = t2.type_id
ORDER BY t1.id desc 
LMIT 4;

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