MySQL-如何獲取按特定字段分組的最新行值？

Question

假設我們有一個名為表A的表

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

您如何獲取按外國ID分組的最新行（我們將以id的順序為基礎）？ 基本上，我想得到的是

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

Answer 1

試試這個查詢

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

將#temp替換為您的實際表名。

Answer 2

試試這個查詢

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

如果還需要值，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

小提琴

Answer 3

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演示

OUTPUT

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

Answer 4

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

對於少量結果，此ans很好，但是如果您使用大量數據，則僅“值”字段的值可能會錯誤。 另一種方法是使您獲得適當的價值更好，這是此代碼。

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