sql assign a category id when using order by

I'm new to SQL.

When I order by SomeData on my table I get:

ID      SomeData
6       ABC
3       ABC
12      FG
1       FH
2       GI
4       JU
8       K3
5       K3
11      P7

great. but what i really want on output is

ID      Category
6       1
3       1
12      2
1 开发者_如何学JAVA      3
2       4
4       5
8       6
5       6
11      7

That is every time SomeData changes on the sort I want to increment Category by one

I can't see how to do this. Any help would be greatly appreciated. Thanks.

If you are on SQL-Server, you can use the DENSE_RANK() ranking function in combination with OVER:

SELECT ID
     , DENSE_RANK() OVER (ORDER BY SomeData)
       AS Category
FROM myTable
ORDER BY SomeData

See: SQL-Server: Ranking Functions

SELECT ROW_NUMBER() OVER(ORDER BY SomeData ASC) AS Category, otherfield1..