MySQL - 如何获取按特定字段分组的最新行值？

Question

比方说，我们有这个表名为表一

id   foreign_id value 
1    1   x 
2    2   y 
3    1   y 
4    2   x 
5    3   x 

其中id是主键

你如何获得最新的行（我们将在id的以立足本）分组由外国身份证？基本上，我想是

id  foreign_id  value 
3  1    y 
4  2    x 
5  3    x 

Answer 1

尝试此查询

SELECT max(id) AS ID, foreign_id FROM tbl 
GROUP BY foreign_id 

如果还需要值，那么

SELECT a.ID, a.foreign_id, a.value 
FROM tbl a, 
(SELECT max(id) AS ID, foreign_id 
     FROM tbl GROUP BY foreign_id) b 
WHERE a.id = b.id AND 
     a.foreign_id = b.foreign_id 

FIDDLE

Answer 2

SELECT a.* 
FROM tableName a 
     INNER JOIN 
     (
      SELECT foreign_ID, max(id) max_ID 
      FROM tableName 
      GROUP BY foreign_ID 
     ) b ON a.foreign_ID = b.foreign_ID AND 
       a.ID = b.max_ID 

• SQLFiddle Demo

输出

╔════╦════════════╦═══════╗ 
║ ID ║ FOREIGN_ID ║ VALUE ║ 
╠════╬════════════╬═══════╣ 
║ 3 ║   1 ║ y  ║ 
║ 4 ║   2 ║ x  ║ 
║ 5 ║   3 ║ x  ║ 
╚════╩════════════╩═══════╝ 

Answer 3

尝试此查询，

SELECT t.id, t.foreign_id, t.value FROM #temp t 
WHERE t.id IN (SELECT max(id) FROM #temp GROUP BY foreign_id) 

替换#temp与实际的表名。

Answer 4

`SELECT MAX(id) AS ID, 
     foreign_id, 
     value 
FROM tbl 
GROUP BY foreign_id ASC` 

这个ans对于少量的结果来说相当好，但是如果你使用大量的数据，那么它可能只对“value”字段有错误的值。另一种方法更适合你获得适当的价值，这里是这个代码。

`SELECT MAX(id) AS ID, 
     foreign_id, 
     value 
FROM tbl 
WHERE id in (SELECT MAX(id) FROM tbl) 
GROUP BY foreign_id ASC`