Question

我有一个查询：

SELECT ID, Name, EventTime FROM table
    WHERE Name = 'value1' AND EventTime < timeValue1
       OR Name = 'value2' AND EventTime < timeValue2
       OR Name = 'value3' AND EventTime < timeValue3
       ...
ORDER BY EventTime DESC

每个条件Name = ... AND EventTime < ...可以返回多行，但是根据OR子句，我只需要每个ORDER BY条件的第一行。

有什么方法可以实现这一目标或解决方法吗？

Answer 1

在我看来您正在搜索row_number（）

  select * from (  SELECT ID, Name, EventTime
    , row_number() over(partition by Name order by  EventTime DESC) rn  FROM table
    WHERE Name = 'value1' AND EventTime < timeValue1
       OR Name = 'value2' AND EventTime < timeValue2
       OR Name = 'value3' AND EventTime < timeValue3
       ...
  ) a where a.rn=1

Answer 2

;
WITH A
AS
(
    SELECT *, ROW_NUMBER()OVER(PARTITION BY [GROUP] ORDER BY 1) as RN
    FROM 
    (
            SELECT ID, Name, EventTime,  
            CASE WHEN Name = 'value1' AND EventTime < timeValue1 THEN '1'
                 WHEN Name = 'value2' AND EventTime < timeValue2 THEN '2'
                 WHEN Name = 'value3' AND EventTime < timeValue3 THEN '3'
                 WHEN Name = 'value3' AND EventTime < timeValue4 THEN '4'
                 --Could be more here
                 END as [Group]
            FROM table
    )
) 
SELECT * FROM A WHERE RN = 1
ORDER BY EventTime DESC

Answer 3

我想我会这样处理：

SELECT ID, Name, EventTime
FROM (SELECT t.*,
             ROW_NUMBER() OVER (PARTITION BY name ORDER BY t.eventtime DESC) as seqnum
      FROM table t JOIN
           (VALUES ('value1', timevalue1), ('value2', timevalue2), ('value3', timevalue3)
           ) v(name, timevalue)
           ON t.name = v.name and t.eventtime < v.timevalue
     ) t
WHERE seqnum = 1
ORDER BY EventTime DESC;

我更喜欢将派生表用于此类重复值，而不是将其嵌入查询逻辑中。

Answer 4

您可以尝试：

SELECT Top (1) ID, Name, EventTime FROM table
    WHERE Name = 'value1' AND EventTime < timeValue1
       OR Name = 'value2' AND EventTime < timeValue2
       OR Name = 'value3' AND EventTime < timeValue3
       ...
ORDER BY EventTime DESC

Answer 5

只要您的所有列名都相同，就可以使用联合。

SELECT top 1 ID, Name, EventTime FROM table
WHERE Name = 'value1' AND EventTime < timeValue1
ORDER BY EventTime DESC
UNION
SELECT top 1 ID, Name, EventTime FROM table
WHERE 
    Name = 'value2' AND EventTime < timeValue2
ORDER BY EventTime DESC
UNION
SELECT top 1 ID, Name, EventTime FROM table
WHERE 
    Name = 'value3' AND EventTime < timeValue3
ORDER BY EventTime DESC

编辑：有多余的或声明，将其删除。

每个“ OR”条件的第一行

5 个答案: