How Can I Generate Accurate Date Series Across Multiple Years in PostgreSQL?

Accurately generate PostgreSQL date series spanning multiple years

The generate_series function is useful when generating a date sequence between two given dates in PostgreSQL. However, as the query below shows, it may not provide accurate results when dates span different years:

<code class="language-sql">select date '2004-03-07' + j - i as AllDate 
from generate_series(0, extract(doy from date '2004-03-07')::int - 1) as i,
     generate_series(0, extract(doy from date '2004-08-16')::int - 1) as j</code>

To solve this problem, a more precise solution can be used, which involves the conversion of timestamps:

<code class="language-sql">SELECT date_trunc('day', dd):: date
FROM generate_series
        ( '2007-02-01'::timestamp 
        , '2008-04-01'::timestamp
        , '1 day'::interval) dd
        ;</code>

In this query, the date_trunc function is used to extract the date portion from the generated timestamp, ensuring accurate results even if the dates span different years. The generate_series function creates a sequence of timestamps spaced one day apart, and then the date_trunc function converts these timestamps back to dates, thus providing a reliable date sequence.

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