Question

我有一个包含以下语法的表：

ID, VALUE, TIMESTAMP

(ID,TIMESTAMP)是主键，因此每个ID可能有多行。有5000个独特的ID。

我想检索每个ID的最新条目。

我天真的做法是： SELECT * FROM table ORDER BY TIMESTAMP DESC LIMIT 5000;

对于大多数情况，这将给出正确的结果，但不能保证。

因为表中可能有100k到500k条目，所以我想考虑性能。

你有什么建议？

Answer 1

尝试这个

SELECT ID, VALUE, TIMESTAMP 
  FROM table 
  GROUP BY ID 
  HAVING MAX(TIMESTAMP)
  ORDER BY TIMESTAMP DESC ;

OR

SELECT ID, VALUE, TIMESTAMP 
  FROM table 
  GROUP BY ID 
  ORDER BY TIMESTAMP DESC ;

Answer 2

你会找到每个ID条目的最新日期，试试这个

SELECT *
FROM table AS a
WHERE TIMESTAMP = (
    SELECT MAX(TIMESTAMP)
    FROM table AS b
    WHERE a.ID = b.ID
  )

Answer 3

Please try this :

SELECT * FROM 
(SELECT ID,
       VALUE,
    ROW_NUMBER() OVER(PARTITION BY ID ORDER BY TIMESTAMP DESC) AS TIMESTAMP
    FROM
    TABLE )
    WHERE TIMESTAMP=1 ;

If your DB supports QUALIFY statement you can try below also :

SELECT * FROM
        TABLE
    QUALIFY ROW_NUMBER() OVER(PARTITION BY ID ORDER BY TIMESTAMP DESC)=1 ;`enter code here`

区别于一列，但检索全部

3 个答案: