如何在更新语句条件下使用计数？

问题描述

我们有两个表，Bucket和Student。我们必须在具有相同国家和城市的学生表中更新Bucket_id。但是在我的Bucket表中，我有两个针对相同国家和城市的Bucket ID，我们可以通过Desc来区分它们。

当我们在“学生”表中更新Bucket_id时，请牢记只能将70个学生分配给同一存储桶ID的时间。分配了70个学生后，它将使用另一个存储段ID更新

Bucket Table
BucketId  Desc    Country  City
1         SOUTH    PAK     KHI
2         NORTH    PAK     KHI

Student中最初的Bucket_Id为空

预期结果如下：更新学生表中的Bucket_Id之后

  Student Table
  StudentId  Country  City  BucketId
  101           PAK     KHI   1
  102           PAK     KHI   1
  109           PAK     KHI   1
  201           PAK     KHI   2

我尝试使用

update student std set Bucket_Id = (
select bucket_id from Bucket b where b.country=std.country and b.city = std.city and count(std.bucket_id) < 70
);

我们该怎么做？我们正在使用oracle 11g。

解决方法

您可以使用查询分配存储桶：

select s.*,b.bucketid
from (select s.*,row_number() over (partition by country,city order by studentid) - 1 as seqnum
      from students s
     ) s join
     (select b.*,city order by bucketid) - 1 as seqnum
      from buckets b
     ) b
     on s.seqnum between b.seqnum * 70 and (b.seqnum + 1) * 70 - 1;

Oracle在update中没有很好的支持跨表处理更新，因此您需要使用merge：

merge into
    students s using
    (select s.*,b.bucketid
     from (select s.*,city order by studentid) - 1 as seqnum
           from students s
          ) s join
          (select b.*,city order by bucketid) - 1 as seqnum
           from buckets b
          ) b
          on s.seqnum between b.seqnum * 70 and (b.seqnum + 1) * 70 - 1
    ) ss
    on s.studentid = ss.studentid
when matched then update
    set s.bucketid = ss.bucketid;

,

看看这是否对您有用：

update students std set BucketId = (
select  min(bucketid) from Bucket b where b.country=std.country and b.city = std.city)
where bucketid is null
and std.STUDENTID in (
SELECT x.STUDENTID FROM 
(
select StudentId,rank() over(partition by country,city order by StudentId) rn  
from students 
)  x where rn <= 3);

,

如果我正确理解了问题，也可以尝试以下方法：

MERGE INTO student t
USING (
SELECT
  studentid,CAST( 
    ROW_NUMBER() OVER(
      PARTITION BY country,city 
      ORDER BY studentid
    ) / 70 + 0.5 
  AS NUMBER(9,0) 
  ) AS bucketid
FROM student
) s
  ON (t.studentid=s.studentid)
WHEN MATCHED THEN UPDATE
SET bucketid = s.bucketid