如何更新列的每个数据？

Question

我有一个表名为类

|Record_No [PK] | Student_No | Class_No | Seat_No | 
===================================================== 
|1    | 200910  | 2   | 20  | 
|2    | 2| 2   | 13  | 
|3    | 200965  | 2   | 1  | 
|4    | 200920  | 2   | 8  | 
|5    | 200911  | 2   | 9  | 
|6    | 200955  | 1   | 10  | 
|7    | 200924  | 1   | 9  | 
|8    | 200922  | 1   | 1  | 
|9    | 200901  | 2   | 11  | 
|10    | 200902  | 2   | 18  | 

是否有可能更新Seat_No的数字从1级多达座位的最后一算没有其类不等于2？

表应该是这样的：

|Record_No [PK] | Student_No | Class_No | Seat_No | 
===================================================== 
|1    | 200910  | 2   | 1  | 
|2    | 2| 2   | 2  | 
|3    | 200965  | 2   | 3  | 
|4    | 200920  | 2   | 4  | 
|5    | 200911  | 2   | 5  | 
|6    | 200955  | 1   | 10  | 
|7    | 200924  | 1   | 9  | 
|8    | 200922  | 1   | 1  | 
|9    | 200901  | 2   | 6  | 
|10    | 200902  | 2   | 7  | 

截至目前，我只能通过

UPDATE class SET Seat_No = 1 WHERE Class_No = 2 AND Student_No = 200910; 
UPDATE class SET Seat_No = 2 WHERE Class_No = 2 AND Student_No = 2; 
... 

等实现这个..

我怎样才能解决这个没有把每个student_no放在查询中？请帮助。

Answer 1

假设你Record_No是你的榜样1-5，您可以使用它：

UPDATE class SET Seat_No = Record_No WHERE Class_No = 2 

如果不是，它取决于你的RDBMS。

这里是PostgreSQL的做法：

UPDATE Class C 
SET  Seat_No = t.rn 
FROM (
     SELECT Record_No, ROW_NUMBER() OVER (ORDER BY Record_No) rn 
     FROM Class 
     WHERE Class_no = 2 
     ) t 
WHERE C.Record_No = t.Record_No 

SQL Fiddle Demo

Answer 2

update class 
set seat_no = s.rn 
from (
    select 
     row_number() over(order by record_no) rn, 
     record_no 
    from class 
    where class_no = 2 
) s 
where class.record_no = s.record_no 

如果要更新所有类：

update class 
set seat_no = s.rn 
from (
    select 
     row_number() over(partition by class_no order by record_no) rn, 
     record_no 
    from class 
) s 
where class.record_no = s.record_no