关联子查询出错

Question

我有一个包含2列的表格：Horse和RaceDate。我想创建第三列，为每匹马显示每个RaceDate的30天内的Racedate数量，比每个Racedate的30天内少。我正在尝试通过相关的子查询来做到这一点，但是因为我正在将一个字段与选择的2个字段进行比较，所以显然不起作用。我真的不想恢复为将其视为游标，对此有解决方案吗？

select I.Last30Days,O.Horse,O.RaceDate from Rep2.AuditTrail O
where dateadd(d,-30,O.Racedate) > select I.RaceDate, count(I.RaceDate) as 
Last30Days
from Rep2.AuditTrail I
where I.Horse = O.Horse
group by I.RaceDate

Answer 1

如果我的理解正确，您可以使用CROSS APPLY进行修改。

create table AuditTrail (
  Horse varchar(50),
  Racedate date
);

INSERT INTO AuditTrail VALUES ('AA','2018-01-01');
INSERT INTO AuditTrail VALUES ('AA','2018-02-01');
INSERT INTO AuditTrail VALUES ('AA','2018-03-08');
INSERT INTO AuditTrail VALUES ('AA','2018-04-01');

查询1 ：

select O.Horse,O.Racedate,COUNT(Last30Days) Last30Days
from Rep2.AuditTrail O 
CROSS APPLY (
    select I.RaceDate as Last30Days
    from Rep2.AuditTrail I
    where I.Horse = O.Horse AND  DATEDIFF(DAY,i.RaceDate,O.RaceDate)>30
) t1
group by O.Horse,O.Racedate

Results ：

| Horse |   Racedate | Last30Days |
|-------|------------|------------|
|    AA | 2018-02-01 |          1 |
|    AA | 2018-03-08 |          2 |
|    AA | 2018-04-01 |          2 |

Answer 2

使用“选择”中的子查询尝试该查询

select 
  O.Horse,
  O.RaceDate, 
  ( Select Count(*) 
    From AuditTrail 
    Where Horse=O.Horse 
      and DATEDIFF(DAY,RaceDate,O.RaceDate)<=30 ) as Last30Days
from Rep2.AuditTrail O