U-SQL 是否接受使用多个 FIRST_VALUE 来删除特定列中的重复项？

Question

我有一个 table，其中多行是重复的，因为两个日期列的值不同。

我想知道是否接受像这样在两列中使用 FIRST_VALUE，以删除指定列上的重复项：

SELECT
 EmployeeName,
 FIRST_VALUE(StartDateTime) OVER(ORDER BY UpdatedDateTime DESC) AS StartDateTime,
 FIRST_VALUE(UpdatedDateTime) OVER(ORDER BY UpdatedDateTime DESC) AS UpdatedDateTime 
 FROM @Employees;

Answer 1

如果您需要删除某些字段的重复项，您需要使用 ROW_NUMBER() 和 CTE:

-- Sample data: dates duplicates
declare @t table (id int, dt date);
insert into @t values
(1, '2018-01-14'),
(1, '2018-01-14'),
(1, '2018-01-15'),
(1, '2018-01-15');
with cte as (
    select *,
           -- assign row number for each partition consisting of same date
           row_number() over (partition by dt order by dt) as cnt
    from @t
)
-- we're interested only in one row (i.e. first)
select id, dt from cte where cnt = 1;

/*
 Output:
+-------+---------+
| id | dt         |
+----+------------+
|  1 | 2018-01-14 |
|----|------------|
|  1 | 2018-01-15 |
+----+------------+
*/

U-SQL 是否接受使用多个 FIRST_VALUE 来删除特定列中的重复项？

U-SQL Is it accepted to use more than one FIRST_VALUE to remove duplicates in specific columns?

sql

u-sql