Row counter per Column - mysql

Question

Say I have a table like so
| id | user_id | event_id | created_at |
|----|---------|----------|------------|
| 1 | 5 | 10 | 2015-01-01 |
| 2 | 6 | 7 | 2015-01-02 |
| 3 | 3 | 8 | 2015-01-01 |
| 4 | 5 | 9 | 2015-01-04 |
| 5 | 5 | 10 | 2015-01-02 |
| 6 | 6 | 1 | 2015-01-01 |
I want to be able to generate a counter of events per user. So my result would be:
| counter | user_id | event_id | created_at |
|---------|---------|----------|------------|
| 1 | 5 | 10 | 2015-01-01 |
| 1 | 6 | 7 | 2015-01-02 |
| 1 | 3 | 8 | 2015-01-01 |
| 2 | 5 | 9 | 2015-01-04 |
| 3 | 5 | 10 | 2015-01-02 |
| 2 | 6 | 1 | 2015-01-01 |

Answer 1

One idea is to self join the table and group by to replicate row_number() over.. function available in other RDBMS.
Check this Rextester Demo and see second query, to understand how inner join works in this case.
select t1.user_id,
t1.event_id,
t1.created_at,
count(*) as counter
from your_table t1
inner join your_table t2
on t1.user_id=t2.user_id
and t1.id>=t2.id
group by t1.user_id,
t1.event_id,
t1.created_at
order by t1.user_id,t1.event_id;
Output:
+---------+----------+------------+---------+
| user_id | event_id | created_at | counter |
+---------+----------+------------+---------+
| 3 | 8 | 01-01-2015 | 1 |
| 5 | 10 | 01-01-2015 | 1 |
| 5 | 10 | 02-01-2015 | 3 |
| 5 | 9 | 04-01-2015 | 2 |
| 6 | 1 | 01-01-2015 | 2 |
| 6 | 7 | 02-01-2015 | 1 |
+---------+----------+------------+---------+

Answer 2

Try the following:
select counter,
xx.user_id,
xx.event_id,
xx.created_at
from xx
join (select a.id,
a.user_id,
count(*) as counter
from xx as a
join xx as b
on a.user_id=b.user_id
and b.id<=a.id
group by 1,2) as counts
on xx.id=counts.id
Use a join to generate rows for each id with all the other lower ids for that user below it and count them.

Answer 3

Try This one:
Sub query will help to get this rsult.
select (select count(*) from user_event iue where iue.user_id == oue.user_id) as counter,
oue.user_id,
oue.event_id,
oue.created_at
from user_event oue

Answer 4

You could try to use a variable as a table, cross join it with the source table and reset whenever user id changes.
SELECT #counter := CASE
WHEN #user = user_id THEN #counter + 1
ELSE 1
END AS counter,
#user := user_id AS user_id,
event_id,
created_at
FROM your_table m,
(SELECT #counter := 0,
#user := '') AS t
ORDER BY user_id;
I've created a demo here