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Overview

The DATE_TRUNC() function truncates intervals or timestamps/time zones to a specified field. The return type is the same as the source type.

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Syntax

The syntax for using the DATE_TRUNC() function is as follows:

DATE_TRUNC(field, source);

or

DATE_TRUNC(field, source, time_zone);

Let’s analyze the above syntax:

  • field: The unit of time used to truncate the source value. It accepts text inputs and is case-insensitive.
  • source: The value you want to truncate. It can be INTERVAL, TIMESTAMP, or TIMESTAMP WITH TIME ZONE.
  • time_zone (applicable for the second syntax option): The time zone for the operation. It accepts text input.

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Fields

Below is a list of supported values to specify the fields param in DATE_TRUNC() syntax.

  • microseconds
  • milliseconds
  • second
  • minute
  • hour
  • day
  • week
  • month
  • quarter
  • year
  • decade
  • century
  • millennium

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Examples

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Case #1: Truncating to Year

This example truncates the timestamp to the year level.

select DATE_TRUNC('year', '1911-12-02 19:40:00'::timestamp);

The timestamp **“1911-12-02 19:40:00” **has been truncated to 1911, with the month and day set to January 1st. 

         date_trunc         
----------------------------
 1911-01-01 00:00:00.000000

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Case #2: Truncating to Day

This query truncates the timestamp “1911-12-02 19:40:00” to the day level.

select DATE_TRUNC('day', '1911-12-02 19:40:00'::timestamp);

The timestamp has been truncated to the same day, year, month, and day components. 

        date_trunc         
----------------------------
 1911-12-02 00:00:00.000000

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Case #3: Truncating to Week

This query truncates the timestamp “1911-12-02 19:40:00” to the week level.

select DATE_TRUNC('week', '1911-12-02 19:40:00'::timestamp);

The timestamp has been truncated to the week starting on November 27, 1911. 

        date_trunc         
----------------------------
 1911-11-27 00:00:00.000000

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Case #4: Truncating to Quarter

This query truncates the timestamp “1911-12-02 19:40:00” to the quarter level.

select DATE_TRUNC('quarter', '1911-12-02 19:40:00'::timestamp);

The year component of the timestamp is truncated, but the month and day components are set to the beginning of the quarter.

        date_trunc         
----------------------------
 1911-10-01 00:00:00.000000

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Case #5: Truncating to Hour

This query truncates the interval of “15 hours 10 minutes” to the hour level.

select DATE_TRUNC('hour', '15 hour 10 minutes'::interval);

The interval** **has been truncated to 15 hours, with the minutes and seconds set to zero.

   date_trunc    
-----------------
 15:00:00.000000

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Case #6: Truncating to Quarter (Interval)

This query truncates the interval “16 years 4 months” to the quarter level.

select DATE_TRUNC('quarter', '16 years 4 months'::interval);

The interval has been truncated to the nearest quarter.

   date_trunc    
-----------------
 16 years 3 mons