How to Generate Accurate Time Series in PostgreSQL Across Multiple Years?

Generate precise time series in PostgreSQL across multiple years

Generating time series is crucial in many data analysis tasks. In PostgreSQL, the generate_series function can be used to create a range of dates between two given dates. However, the standard approach may fail when dates span multiple years.

Problem Statement

This function may produce incorrect results if generate_series the start and end dates in the query are from different years. For example, when trying to generate a sequence between '2007-02-01' and '2008-04-01', a standard query may produce an invalid set of dates.

Solution

To solve this problem, an improved method is needed. Instead of converting the date to an integer (as in the initial query), we can use the timestamp directly. This allows us to accurately account for transitions between years.

The following modified query generates a time series between any two given dates, regardless of whether they belong to the same year:

<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>

By converting dates to timestamps, we ensure that the calculation of the time difference and subsequent creation of the time series takes the change in years into account. This will generate the correct set of dates for the specified range.

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