根据SQL中的另一个变量选择最大值

Question

I am trying to create an accurate count of student enrollment. There is an individual record for every course registration and any change to that particular course registration results in another record with an incremental sequence number. My table looks something like this:

ID    Course Number   Sequence Number
1     B101            1
1     B101            2
1     B101            3
1     C201            1
1     C201            2
2     E215            1
2     J320            1
2     J320            2

I would like to select the max value of sequence number such that every course registration is retained. This would mean that ID 1 would have 2 records. One would be B101 with sequence number=3 and another record for C201 with sequence number=2.

Answer 1

SELECT id, course_number, MAX(sequence_number) FROM table GROUP BY id, course_number;

Answer 2

您应该首先将id上的所有项目分组，然后将它们在Course_Number上分组，并仅显示Sequence_Number的最大值。

select id,Course_Number,max(Sequence_Number) from TblName group by id,Course_Number