I need to realize cumulative summing per each day. 

For example my data set is as follows:

```
buyer | bread | date      |
---------------------------
b1    |   2   | 2018-01-01|
b1    |   3   | 2018-01-02|
b1    |   1   | 2018-01-04|
b2    |   2   | 2018-01-02|

```

I need to get selection as follows:

```
buyer | cum_sum_on_01_01 | cum_sum_on_01_02 | cum_sum_on_01_03 | cum_sum_on_01_04 | cum_sum_on_01_05 |...
----------------------------------------------------------------------------------------------------------
b1    |        2         |        5         |         5        |      6           |       6          |...
b2    |        0         |        2         |         2        |      2           |       2          |...

```

How to do it?