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

A little improvement to the selected answer would be not to have to define those variables. So this query can be solved in just a single statement:

SELECT COUNT(*) cnt, user
FROM (
    SELECT @num := @num + (@name != user) as number,
           @name := user as user
    FROM t, (select @num := 0, @name := '') as s
    ORDER BY id
) x
GROUP BY number

Output:

| CNT |     USER |
|-----|----------|
|   3 | zhangsan |
|   3 |     lisi |
|   2 | zhangsan |

Fiddle here

Answer 2

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);

Answer 3

if in sql server, oracle, db2...

    with x as(  
select c.*, rn = row_number() over (order by c.id)
  from test c 
  left join test n
    on c.[user] = n.[user]
   and c.[id] + 1 = n.[id]   
 where n.id is null
)
select a.[user], a.id - coalesce(b.id, 0) 
  from x a
  left join x b
    on a.rn = b.rn + 1 

Answer 4

I think what you are looking for is to COUNT(ID):

SELECT COUNT(ID) FROM table GROUP BY user

Answer 5

You cannot do this in sql without doing some sort of sequential (iterative) analysis. Remember sql is set operation language.

Answer 6

If you try:

SET @name:='',@num:=0;

SELECT id,
       @num:= if(@name = user, @num, @num + 1) as number,
       @name := user as user
FROM foo
ORDER BY id ASC;

This gives:

+------+--------+------+
| id   | number | user |
+------+--------+------+
|    1 |      1 | a    |
|    2 |      1 | a    |
|    3 |      1 | a    |
|    4 |      2 | b    |
|    5 |      2 | b    |
|    6 |      2 | b    |
|    7 |      3 | a    |
|    8 |      3 | a    |
+------+--------+------+

So then you can try:

SET @name:='',@num:=0;

SELECT COUNT(*) as count, user
FROM (
SELECT @num:= if(@name = user, @num, @num + 1) as number,
       @name := user as user
FROM foo
ORDER BY id ASC
) x
GROUP BY number;

Which gives

+-------+------+
| count | user |
+-------+------+
|     3 | a    |
|     3 | b    |
|     2 | a    |
+-------+------+

(I called my table foo and also just used names a and b because I was too lazy to write zhangsan and lisi over and over).