如何通过显示最新数据行来使用Group

如果每组只需要最新的一个:

SELECT somefield
FROM table t1
WHERE timestamp = (SELECT MAX(timestamp)
                   FROM table t2
                   WHERE t1.somefield = t2.somefield);

或者只是最近的一个:

SELECT somefield
FROM table
GROUP BY somefield
ORDER BY MAX(timestamp) DESC
LIMIT 1;

我想你在找 ORDER BY 条款。

SELECT Foo.Bar, Foo.SomeTimestamp
FROM Foo
ORDER BY Foo.SomeTimestamp DESC

如果按列分组,则可能返回聚合数据。如果时间戳对于每行聚合数据都是唯一的,则可能需要使用 MAX 函数(或类似函数)为每个组返回一个时间戳。例如:

SELECT Foo.TypeID, SUM(Foo.Price) AS Price, MAX(Foo.OrderDate) AS LastOrder
FROM Foo
GROUP BY Foo.TypeID
ORDER BY MAX(Foo.OrderDate) DESC

如果只需要第一行,可以使用 LIMIT 条款:

SELECT Foo.Bar, Foo.SomeTimestamp
FROM Foo
ORDER BY Foo.SomeTimestamp DESC
LIMIT 0, 1

这从第0行开始,最多返回1行。