sql - mysql obtain running difference -


i have below table structure , data:

----------------------------- |  date      | accu. output | ----------------------------- | 2017-01-01 |          150 | | 2017-01-02 |          165 | | 2017-01-03 |          182 | | 2017-01-04 |          190 | | 2017-01-05 |          210 | -----------------------------

i need generate below output above dataset. can client side processing. trying write query this.

---------------------------------------------- |  date      |   accu. output | daily output | ---------------------------------------------- | 2017-01-05 |            210 |           20 | | 2017-01-04 |            190 |            8 | | 2017-01-03 |            182 |           17 | | 2017-01-02 |            165 |           15 | | 2017-01-01 |            150 |            0 | ----------------------------------------------

daily output difference between current accu. output , previous day's accu. output.

thanks

here method uses left join:

select t.*,        coalesce(t.accu_output - tprev.accu_output, 0) diff t left join      t tprev      on tprev.date = t.date - interval 1 day;

this assumes -- in sample data -- days increasing no gaps , 1 value per day. these conditions implied question (previous day's output).


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