PostgreSQL date_part: Syntax & 7 Use Cases Simplified

PostgreSQL is a robust object-relational database system that is open source and free. Its proven design and more than 30 years of active development have given it a solid reputation for dependability, data integrity, and correctness.

In this article, you will gain information about PostgreSQL date_part Function. You will also gain a holistic understanding of PostgreSQL, its key features, and different use cases of PostgreSQL date_part Function.

Read along to find out in-depth knowledge about PostgreSQL date_part – Syntax & 7 Use Cases.

What is PostgreSQL?

PostgreSQL an open-source, high-performance relational database, is notable for having a platform that supports numerous RDBMS features. In addition to RDBMS functionality, it offers indexes, views, stored procedures, triggers, atomicity features, etc. It also supports JSON and SQL queries. 

PostgreSQL supports a wide range of operating systems, including Windows, Linux, macOS, UNIX, etc. PostgreSQL’s source code is publicly available under an open-source license, allowing users to use, change, and customize it to suit their needs. With PostgreSQL, there is no risk of over-deployment because there is no license fee.

Key Features of PostgreSQL

• Customizable: Plugins can be created to modify PostgreSQL to suit your needs. It also makes it possible to include special functions developed in a variety of programming languages, such as Java, C, C++, etc.
• Supportive Community: A dedicated community is always there for its users. A large range of private, third-party support services is compatible with PostgreSQL.
• Open-Source: PostgreSQL is a free and open-source database system that supports both relational and object-oriented databases.
• Users: It is a popular and widely used RDBMS. Many businesses utilize PostgreSQL, including Apple, Etsy, Facebook, Instagram, etc.
• Code quality: PostgreSQL’s whole development cycle is community-driven, enabling quick issue reporting and verification. A group of experts reviews each line of code that is added to PostgreSQL.
• Data Availability and Resiliency: PostgreSQL versions offer extra availability, resilience, and security for mission-critical production systems, such as those found in governmental organizations, financial institutions, and healthcare providers, despite being privately supported.

You can also take a look at the PostgreSQL Now() Function to explore other useful functions of PostgreSQL

What is PostgreSQL date_part?

• Key Function
• Syntax

Key Function

PostgreSQL includes a number of functions for working with dates. These functions can be used to convert a particular string to a date, simply to get the current system date or evaluate the difference between two dates. However, for converting a string to a date you may want to provide a timestamp and convert it to a date. To streamline this, PostgreSQL provides several functions that allow you to convert any given timestamp to date in an efficient manner and perform computations thereafter.

In SQL Server datediff function is used whereas in PostgreSQL another function called date_part determines the difference between two DateTime values (in seconds, minutes, hours, days, weeks, or months). However, there is a workaround. The date_part function extracts the date or time’s subfields, such as seconds, minutes, hours, days, etc. 

By using the PostgreSQL date_part function we can obtain the difference between two dates depending on their provided intervals. Because here PostgreSQL date_part serves as a calendar and is particularly beneficial to users & crucial to the database management system. According to query syntax, certain PostgreSQL date_part methods use the system’s current date.

Syntax

date_part(subfield,source)

The subfield serves as an identifier to choose which subfield should be extracted from the source. The source can be a date, timestamp, interval, etc.

Whereas, the values that can be entered into the subfield are as follows: 

• century
• decade
• year
• month
• day
• hour
• minute
• second
• microseconds
• milliseconds
• dow
• doy
• epoch
• isodow
• timezone
• timezone_hour
• timezone_minute

For instance: After execution of the below-mentioned code year part (2022) of the date ‘2022-10-18’ is extracted & obtained as an output.

SELECT date_part('year',date'2022-10-18');
------OUTPUT------
2022

PostgreSQL date_part : 7 Example Use Cases

• PostgreSQL date_part in Days
• PostgreSQL date_part in Hours
• PostgreSQL date_part in Minutes
• PostgreSQL Date Difference in Milliseconds
• PostgreSQL date timestamp difference
• PostgreSQL date_part in months
• PostgreSQL  date_part in seconds

PostgreSQL date_part in Days

Let’s look at an example to better understand how to use the date_part function in PostgreSQL to compute the number of days that separate two dates.

SELECT date_part('day','2022-01-15'::timestamp - '2022-01-01'::timestamp) as days;
------OUTPUT------
14

In the code above, we are counting the days between the date ‘2022-01-15’ and ‘2022-01-01’. Here, “:: timestamp” indicates that we are using the typecast operator to convert the date string to the timestamp data type (::). The day difference between the two dates is 14 days as shown in the output above.

PostgreSQL date_part in Hours

Using the PostgreSQL date_part function, we can also determine the date difference in hours.

To get the number of hours between two dates, refer to the example given below.

SELECT date_part('day','2022-10-18 10:50'::timestamp - '2022-10-17 08:15'::timestamp) * 24 +
date_part('hour','2022-10-18 10:50'::timestamp - '2022-10-17 08:15'::timestamp) as hours;
------OUTPUT------
26

In the above output obtained, the hour’s difference between the ‘2022-10-18 10:50’ and ‘2022-10-17 08:15’ dates is correctly identified as 26 hours.

PostgreSQL date_part in Minutes

To calculate the date difference in minutes, PostgreSQL date_part  function can be employed.

Let’s refer to the below-mentioned code snippet to understand.

SELECT
date_part('hour','2022-10-18 07:50'::timestamp - '2022-10-18 04:15'::timestamp) * 60 +
date_part('minute', '2022-10-18 07:50'::timestamp - '2022-10-18 04:15'::timestamp ) as minutes;
------OUTPUT------
215

In the above code, we first have to calculate the hours between ‘2022-10-18 07:50’ and ‘2022-10-18 04:15’, then multiply it by 60 (1hr = 60 mins). Thereafter, add the exact minute’s difference to it from the second date_part function. After the complete execution, the output obtained is 215 minutes.

PostgreSQL Date Difference in Milliseconds

We’ll use PostgreSQL’s extract function to determine the date difference in milliseconds.

The example of the date difference in milliseconds is as follows:

SELECT EXTRACT(MILLISECONDS FROM TIME '22:22:22.5')- EXTRACT(MILLISECONDS FROM TIME '22:20:20.5') as milliseconds;
------OUTPUT------
2000

Here, we have used the extract function to get the desired value of the milliseconds from both dates. After this, we have simply performed the arithmetic difference to get the desired output as 2000.

PostgreSQL Date Timestamp Difference

We will compute the Date timestamp difference using the arithmetic operator minus (-). Let’s have a look at the code:

SELECT ('2022-10-18 20:40:30'::timestamp) - ('2022-10-18 16:15:00'::timestamp) ;

PostgreSQL date_part in Months

Using the date_part function in PostgreSQL, we can also obtain the date difference in months.

SELECT (date_part('year', '2022-11-01'::date) - date_part('year', '2022-01-02'::date)) * 12 +
(date_part('month', '2022-11-01'::date) - date_part('month', '2022-01-02'::date)) as months;
------OUTPUT------
10

In the above code, we first have to calculate the year between ‘2022-11-01’ and ‘2022-01-02’, then multiply it by 12 (1 year = 12 months). Thereafter, add the exact month’s difference to it from the second date_part function. After the complete execution, the output obtained is 10 months.

PostgreSQL date_part in Seconds

The date_part function in PostgreSQL can also be used to compute the date difference seconds.

SELECT (date_part('hour', '10:55:10'::time - '05:55:55'::time) * 60 +
               date_part('minute', '10:55:10'::time - '05:55:55'::time)) * 60 +
               date_part('second', '10:55:10'::time - '05:55:55'::time) as seconds;
------OUTPUT------
17955

In the above code, we first have to calculate the hour gap & minute gap then multiply them by 60 respectively. Thereafter, add the exact second’s difference to it from the second date_part function. After the complete execution, the output obtained is 17955 seconds.

Also, you can take a look at our detailed guide on PostgreSQL – Convert DateTime to Date.

Conclusion

In this article, the complete comprehensive manual for PostgreSQL date_part is provided. After a quick & insightful overview of PostgreSQL introduction and operation, we have deep-dived into PostgreSQL date_part. We have learned about the syntax and fundamental use cases of date_part function.

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