MySQL - 如何獲取按特定字段分組的最新行值？

Question

比方說，我們有這個表名爲表一

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

其中id是主鍵

你如何獲得最新的行（我們將在id的以立足本）分組由外國身份證？基本上，我想是

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

Answer 1

嘗試此查詢

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

如果還需要值，那麼

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

輸出

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

Answer 3

嘗試此查詢，

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

替換#temp與實際的表名。

Answer 4

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

這個ans對於少量的結果來說相當好，但是如果你使用大量的數據，那麼它可能只對「value」字段有錯誤的值。另一種方法更適合你獲得適當的價值，這裏是這個代碼。

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