Question

我正在从数据库中查找信息，以便在datetime列中找到最新时间。有时候，一天中有很多次流程要结束，而我只想查看当天的最新消息。

我尝试了INNER JOIN语句，但是我返回的是MAX Date。

下面的数据示例：

Time                 |    Product
2019-01-01-22:15     |    CHEESE
2019-01-01-22:35     |    CHEESE
2019-01-02-22:35     |    CHEESE
2019-01-02-22:37     |    CHEESE

显示为

Time                 |    Product
2019-01-01-22:35     |    CHEESE
2019-01-02-22:37     |    CHEESE

这将适用于多种产品

*编辑*

我需要一个月的多个日期

*编辑* 当天将用于其他产品，奶酪就是其中的一个例子

所以：

 Time                 |    Product
    2019-01-01-22:15     |    CHEESE
    2019-01-01-22:35     |    CHEESE
    2019-01-01-22:45     |    BREAD
    2019-01-01-22:57     |    BREAD
    2019-01-02-22:35     |    CHEESE
    2019-01-02-22:37     |    CHEESE
    2019-01-02-22:35     |    BREAD
    2019-01-02-22:37     |    BREAD

显示为

Time                 |    Product
2019-01-01-22:35     |    CHEESE
2019-01-01-22:57     |    BREAD
2019-01-02-22:37     |    CHEESE
2019-01-02-22:37     |    BREAD

Answer 1

为什么这还不够？

select product, max(time)
from table t
group by product, cast(t.time as date);

但是，如果您有更多列，则需要subquery：

select t.*
from table t
where t.time = (select max(t1.time)
                from table t1
                where cast(t1.time as date) = cast(t.time as date) and
                      t1.product = t.product
               );

Answer 2

一种选择是在投射时使用top 1 with ties和row_number：

SELECT TOP 1 WITH TIES [Time], Product
FROM TableName
ORDER BY ROW_NUMBER() OVER(
    PARTITION BY Product, CAST([Time] AS Date) 
    ORDER BY CAST([Time] AS Time) DESC)

row_number将在每个日期的最新时间返回1。

另一种选择是使用这样的公用表表达式（或派生表）：

WITH CTE AS
(
    SELECT [Time], 
           Product,
           ROW_NUMBER() OVER(
               PARTITION BY Product, CAST([Time] AS Date) 
               ORDER BY CAST([Time] AS Time) DESC) As Rn
    FROM TableName
)
SELECT [Time], Product
FROM CTE
WHERE Rn = 1

通过这种方式，您可以决定如何订购结果。

Answer 3

尝试一下：

SELECT Product, MAX([Time]) FROM MyTable
GROUP BY Product, CAST([Time] AS DATE)

Answer 4

您可以使用相关子查询：

select t.*
from t
where t.time = (select max(t2.time)
                from t t2
                where convert(date, t2.time) = convert(date, t.time)
               );

选择具有多个DATETIME值的最长日期

4 个答案: