Postgres group by quarter

If someone also needs the year, they can use this:

SELECT (extract(year from published_date)::text || '.Q' || extract(quarter from published_date)::text) as quarter

This will return the value in the form 2018.Q1.

How does it work? It extracts both year and quarter (which are both of type double precision), casts them into strings, and concatenates the whole in something readable.

If you want both quarter and year you can use date_trunc:

SELECT
  date_trunc('quarter', published_date) AS quarter

This gives the date rounded to the start of the quarter, e.g. 2020-04-01, and has the advantage that subsequent steps in the pipeline can read it like a normal date.

(This compares to extract (extract(quarter FROM published_date)), which gives the number of the quarter, i.e. 1, 2, 3, or 4.)

Assuming that the published_date is a date type column you can use the extract function like this:

select 
  topic, 
  person,
  extract(quarter from published_date) as quarter, 
  count(*)
from 
  table1
group by 
  topic, 
  person,
  extract(quarter from published_date)
order by 
  extract(quarter from published_date) asc

Sample SQL Fiddle

If the dates can fall into different years you might want to add the year to the select and group by.