PostgreSQL的选择对于给定的ID

Question

表基本上看起来像最新的条目：

串行ID，ID，日期，数据，数据，数据等

有可能为同一ID多行。我想创建此表的一个视图，用于仅显示每个ID的最新条目的报告。它应该显示所有的列。

有人可以帮助我的SQL选择？谢谢。

Answer 1

有5个不同的方式来做到这一点，但这里有一个：

SELECT * 
FROM yourTable AS T1 
WHERE NOT EXISTS(
    SELECT * 
    FROM yourTable AS T2 
    WHERE T2.ID = T1.ID AND T2.Date > T1.Date 
) 

而这里的另一个：

SELECT T1.* 
FROM yourTable AS T1 
LEFT JOIN yourTable AS T2 ON 
(
    T2.ID = T1.ID 
    AND T2.Date > T1.Date 
) 
WHERE T2.ID IS NULL 

还有一个：

WITH T AS (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY ID ORDER BY Date DESC) AS rn 
    FROM yourTable 
) 
SELECT * FROM T WHERE rn = 1 

好，我是越来越被带走，这是我将发布的最后一个（现在）：

WITH T AS (
    SELECT ID, MAX(Date) AS latest_date 
    FROM yourTable 
    GROUP BY ID 
) 
SELECT yourTable.* 
FROM yourTable 
JOIN T ON T.ID = yourTable.ID AND T.latest_date = yourTable.Date 

Answer 2

这似乎是一个很好的利用了correlated subqueries：

CREATE VIEW your_view AS 
SELECT * 
FROM your_table a 
WHERE date = (
    SELECT MAX(date) 
    FROM your_table b 
    WHERE b.id = a.id 
) 

你的日期列需要唯一标识（如TIMESTAMP类型）的每一行。