Return the first and last value from one column when value from another column changes

Question

I am trying to write a PostgreSQL query to return the first and last dates corresponding to indices. I have a table:

Datetime	Index
March 1 2021	0
March 2 2021	0
March 3 2021	0
March 4 2021	1
March 5 2021	1
March 6 2021	2

In this case, I would want to return:

I am wondering how I would write the PostgreSQL query for this.

Answer 1

I think this can be done with the following:

SELECT MIN("Datetime") AS Start
     , MAX("Datetime") AS End
     , "Index"
  FROM <your_table>
 GROUP BY "Index"
 ORDER BY "Index"
;