sql - Detecting the change on the certain column in the history table -


consider following data:

history.data ======================================= id |data_id| col1  | col2  | date ---+-------+-------+-------+----------- 1  |1      | 123   | 321   | 2017-08-01 2  |1      | 124   | 321   | 2017-08-03 3  |2      | 222   | 555   | 2017-08-05 4  |2      | 242   | 555   | 2017-08-07 5  |2      | 242   | 333   | 2017-08-11

so history_data table keep changes in table. right need date of last change every present entry of data in col1 column. in case desired output should be

data_id | date --------+----------- 1       | 2017-08-03 2       | 2017-08-07

i need in following context:

with cte1 (     select distinct on(data_id)     data_id,     date::date      data d     join history.data hd on hd.data_id = d.id     order d.id, hd.date desc )

so can see, i'm getting date of last record change, regardless of on column change occured.

could please me that?

you can use lag() previous prev_col1 value , prev_col1 <> col1 identify rows change occured:

select distinct on(data_id) * (     select lag(col1) on (partition data_id order d.id) prev_col1,     d.id,     col1,     data_id,     date::date     data d     join history.data hd on hd.data_id = d.id ) t prev_col1 <> col1 or prev_col1 null order id desc

the prev_col1 null condition needed groups 1 member per data_id , assumes first member qualifies change.


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