PostgreSQL query to count/group by day and display days with no data

Question

I need to create a PostgreSQL query that returns

• a day
• the number of objects found for that day

It\'s important that every sing

Answer 1

Extending Gordon Linoff's helpful answer, I would suggest a couple of improvements such as:

• Use ::date instead of date_trunc('day', ...)
• Join on a date type rather than a character type (it's cleaner).
• Use specific date ranges so they're easier to change later. In this case I select a year before the most recent entry in the table - something that couldn't have been done easily with the other query.
• Compute the totals for an arbitrary subquery (using a CTE). You just have to cast the column of interest to the date type and call it date_column.
• Include a column for cumulative total. (Why not?)

Here's my query:

WITH dates_table AS (
    SELECT created::date AS date_column FROM sharer_emailshare WHERE showroom_id=5
)
SELECT series_table.date, COUNT(dates_table.date_column), SUM(COUNT(dates_table.date_column)) OVER (ORDER BY series_table.date) FROM (
    SELECT (last_date - b.offs) AS date
        FROM (
            SELECT GENERATE_SERIES(0, last_date - first_date, 1) AS offs, last_date from (
                 SELECT MAX(date_column) AS last_date, (MAX(date_column) - '1 year'::interval)::date AS first_date FROM dates_table
            ) AS a
        ) AS b
) AS series_table
LEFT OUTER JOIN dates_table
    ON (series_table.date = dates_table.date_column)
GROUP BY series_table.date
ORDER BY series_table.date

I tested the query, and it produces the same results, plus the column for cumulative total.