How to group by week and distinct by day in PostgreSQL

In PostgreSQL, you can group by week and distinct by day using the date_trunc() function in combination with the DATE_PART() function and the GROUP BY clause.

The date_trunc() function is used to truncate a timestamp to a specific precision, in this case, the week. The DATE_PART() function is used to extract a specific part of a timestamp, in this case, the day.

Here’s an example of how you can group by week and distinct by day in PostgreSQL:

SELECT DATE_TRUNC('week', timestamp_column) as week, DATE_PART('day', timestamp_column) as day, COUNT(DISTINCT id)
FROM mytable
GROUP BY week, day
ORDER BY week, day

In this example, the DATE_TRUNC('week', timestamp_column) function is used to truncate the timestamp in the timestamp_column to the week level, and the DATE_PART('day', timestamp_column) function is used to extract the day of the timestamp.

The query will group the results by the truncated week and day, and it will count the distinct values of the id column. The results will be ordered by week and day.

It’s important to note that you can use any column that contains a timestamp, and the query will return the same results regardless of the column used.

You can also use other types of functions like date_part('week', timestamp_column) or date_part('year', timestamp_column), to group by week of year or year respectively.