Question

我有几张桌子，需要加入它们，但有一点麻烦。

表#GradeChange具有学生ID，成绩更改的生效日期以及该日期更改为ON的成绩。表#EventOccurrence包含该学生在特定日期发生的事件。我需要找到学生在活动发生时的成绩。这将是#EventOccurrence生效日期之前#GradeChange的最新成绩。学生可能有多个EventOccurrences，我们可以假设所有学生将至少有一个#GradeChange条目，其日期早于最早的事件。

这是DDL：

    /* If the test table already exists, drop it */
     IF OBJECT_ID('TempDB..#GradeChange','U') IS NOT NULL
        DROP TABLE #GradeChange;

     IF OBJECT_ID('TempDB..#EventOccurrence','U') IS NOT NULL
        DROP TABLE #EventOccurrence;     

/* Create first temp table */ 
 CREATE TABLE #GradeChange 
        (
        ID varchar(6),
        EffectiveDate datetime,
        Grade varchar(50)
        );       

/* Populate it */        
INSERT INTO #GradeChange 
    (ID, EffectiveDate, Grade)
SELECT '678443','Jul  2 2009 11:30PM','Grade 3' UNION ALL
SELECT '678443','Jan 24 2007  2:40PM','Kindergarten - Half Day' UNION ALL
SELECT '678443','Jul  4 2007 11:09PM','Grade 1' UNION ALL
SELECT '678443','Jul  2 2008 11:35PM','Grade 2' UNION ALL
SELECT '718466','May 18 2009 11:50PM','Pre-Kindergarten' UNION ALL
SELECT '718466','Jul  2 2009 11:27PM','Kindergarten - Half Day' UNION ALL
SELECT '718466','Aug 27 2009 11:18PM','Pre-Kindergarten' UNION ALL
SELECT '718466','Jul  9 2010 11:18PM','Kindergarten - Half Day' UNION ALL
SELECT '718466','Aug  2 2010 11:14PM','Kindergarten';

/* Create 2nd temp table */
CREATE TABLE #EventOccurrence
    (
    ID varchar(6),
    EventDate datetime
    ); 

/* Populate it */
INSERT INTO #EventOccurrence
    (ID, EventDate)
SELECT '718466','Nov 16 2010 12:00AM' UNION ALL
SELECT '718466','May 20 2009 12:00AM' UNION ALL
SELECT '678443','Dec  7 2007 12:00AM';

所以这两个表看起来像这样：

Tables Example

预期结果如下：

Results Example

我玩过“MAX”和“MIN”以及“OVER（）”，但不能完全正确。我非常感谢任何帮助！

Answer 1

SELECT  *
FROM    #EventOccurrence eo
OUTER APPLY
        (
        SELECT  TOP 1 Grade
        FROM    #GradeChange gc
        WHERE   gc.id = eo.id
                AND gc.EffectiveDate <= eo.EventDate
        ORDER BY
                gc.EffectiveDate DESC
        ) gc

Answer 2

select eo.ID, eo.EventDate, gc.Grade
    from #EventOccurrence eo
        inner join #GradeChange gc
            on eo.ID = gc.ID
                and gc.EffectiveDate = (select max(gc.EffectiveDate) 
                                            from #GradeChange gc 
                                            where gc.ID = eo.ID 
                                                and gc.EffectiveDate <= eo.EventDate)

Answer 3

with merged (ID, DDate, Grade, pos) AS 
(
    select ID, DDate, Grade, ROW_NUMBER() over (order by ID, DDate) AS pos FROM  (
        select ID, EffectiveDate AS DDate, Grade FROM GradeChange 
        union
        select ID, EventDate AS DDate, NULL FROM EventOccurrence 
    ) sub
) 
SELECT m1.ID, m1.DDate, m2.Grade FROM merged m1 LEFT OUTER JOIN merged m2 ON m1.pos = m2.pos+1 WHERE m1.Grade IS NULL

查询以“最近”加入其他表与日期

3 个答案: