Update all user records in the table and populate low_id 1 to N

Question

i have a table with fields

Table A)

When i run sql command

SELECT  id,
        user,
        `low_id`
FROM    (   SELECT @r:= IF(@u = user, @r + 1,1) AS `low_id`,
                    id,
                    user,
                    @u:= user
            FROM    usertest,
                    (SELECT @i:= 1) AS r,
                    (SELECT @u:= 0) AS u
            ORDER BY user
        ) AS usertest

Table B) I'm getting select in following manner

Id   user    low_ID
--------------------
1    100      1
2    200      1
3    100      Null
4    300      1
5    300      Null
6    100      Null
-------------------

I Want above code to permanently update low_id in sequence 1-n for every user record and then counter resets to 1 for next user and increment low id value by 1 for each record for that user .

I want to Update table A) like table c)

Table C)

Id   user    low_ID
--------------------
1    100      1
2    200      1
3    100      2
4    300      1
5    300      2
6    100      3
-------------------

Answer 1

simple.. order the data by user and count the number of times..

UPDATE users u,
(   SELECT id, if(@a = user, @b:=@b+1, @b:=1) as new_low, @a:= user
    FROM users
    CROSS JOIN(SELECT @a:=0, @b:=1)t
    ORDER BY user, id
) t1
SET u.low_id = t1.new_low
WHERE u.id = t1.id;

DEMO