How to combine near same item by SQL?

Question

I have some data in database:

id user 
1 zhangsan 
2 zhangsan 
3 zhangsan 
4 lisi 
5 lisi 
6 lisi 
7 zhangsan 
8 zhangsan 

I want keep order, a

Answer 1

if in oracle, you can do like below.

SELECT NAME,
       num - lagnum
  FROM (SELECT lagname,
               NAME,
               num,
               nvl(lag(num) over(ORDER BY num), 0) lagnum
          FROM (SELECT id,
                       lag(NAME) over(ORDER BY ID) lagname,
                       NAME,
                       lead(NAME) over(ORDER BY ID) leadname,
                       ROWNUM num
                  FROM (SELECT * FROM test ORDER BY ID))
         WHERE (lagname = NAME AND (NAME <> leadname OR leadname IS NULL))
            OR (lagname IS NULL AND NAME <> leadname)
            OR (lagname <> NAME AND leadname IS NULL)
         ORDER BY ID);