fenix fenix - 4 months ago 18
MySQL Question

Conditional accumulation

it is possible to display accumulated data, resetting the count based on a condition?
I would like to create a script to accumulate if there is value 1 in cell number, but if another value the count should be restarted. Something like what is displayed in the column cumulative_with_condition.

+----+------------+--------+
| id | release | number |
+----+------------+--------+
| 1 | 2016-07-08 | 4 |
| 2 | 2016-07-09 | 1 |
| 3 | 2016-07-10 | 1 |
| 4 | 2016-07-12 | 2 |
| 5 | 2016-07-13 | 1 |
| 6 | 2016-07-14 | 1 |
| 7 | 2016-07-15 | 1 |
| 8 | 2016-07-16 | 2-3 |
| 9 | 2016-07-17 | 3 |
| 10 | 2016-07-18 | 1 |
+----+------------+--------+

select * from version where id > 1 and id < 9;
+----+------------+--------+---------------------------+
| id | release | number | cumulative_with_condition |
+----+------------+--------+---------------------------+
| 2 | 2016-07-09 | 1 | 1 |
| 3 | 2016-07-10 | 1 | 2 |
| 4 | 2016-07-12 | 2 | 0 |
| 5 | 2016-07-13 | 1 | 1 |
| 6 | 2016-07-14 | 1 | 2 |
| 7 | 2016-07-15 | 1 | 3 |
| 8 | 2016-07-16 | 2-3 | 0 |
+----+------------+--------+---------------------------+

Answer

You want something like row_number() (not exactly, but like that). You can do that using variables:

select t.*,
       (@rn := if(number = 1, @rn + 1,
                  if(@n := number, 0, 0)
                 )
       ) as cumulative_with_condition
from t cross join
     (select @n := '', @rn := 0) params
order by t.id;