PostgreSQL – EXTRACT Function

ByAdmin

In PostgreSQL, the EXTRACT function is used to extract specific components (such as year, month, day, hour, etc.) from date and time values. This function allows you to retrieve individual parts of a timestamp or interval.

The basic syntax of the EXTRACT function is as follows: 

EXTRACT(field FROM source);

where field is the part of the date or time that you want to extract (e.g., year, month, day, hour, minute, second);

and source is the date, time, or interval from which you want to extract the specified field.

Below are some examples of using the EXTRACT function:

  1. Extracting the year from a date:
SELECT EXTRACT(YEAR FROM '2023-08-06') AS year;

This query will return the year 2023.

  1. Extracting the month from a timestamp:
SELECT EXTRACT(MONTH FROM TIMESTAMP '2023-08-06 15:30:45') AS month;

This query will return the month 8.

  1. Extracting the day from an interval:
SELECT EXTRACT(DAY FROM INTERVAL '5 days') AS days;

This query will return the number of days 5.

  1. Extracting the hour from the current timestamp:
SELECT EXTRACT(HOUR FROM CURRENT_TIMESTAMP) AS hour;

This query will return the current hour.

You can use various date and time fields with the EXTRACT function, such as:

  • YEAR, MONTH, DAY, HOUR, MINUTE, SECOND: To extract the corresponding components from the date or timestamp.
  • TIMEZONE: To extract the time zone from the timestamp.
  • EPOCH: To extract the number of seconds since January 1, 1970 (UNIX epoch time).

Here’s an example of extracting the time zone and epoch from a timestamp: 

SELECT EXTRACT(TIMEZONE FROM TIMESTAMP '2023-08-06 15:30:45') AS timezone, EXTRACT(EPOCH FROM TIMESTAMP '2023-08-06 15:30:45') AS epoch;

EXTRACT function returns numeric values for most components, but it returns text values for certain components, such as the time zone (e.g., 'UTC', 'America/New_York', etc.).

The EXTRACT function is useful when you need to work with specific date and time components in your PostgreSQL queries or perform calculations based on these components

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