AGE function for differences in PostgreSQL

Introduction

The AGE function helps you find the difference between two dates or times. It tells you how much time has passed between them in years, months, and days.

To find out how old someone is based on their birthdate.

To calculate how long ago an event happened from today.

To measure the time difference between two project deadlines.

To check how long a product has been in stock.

To find the duration between a start date and an end date in reports.

Syntax

PostgreSQL

AGE(timestamp1, timestamp2)
-- or --
AGE(timestamp)

-- timestamp1 and timestamp2 are dates or timestamps
-- If only one timestamp is given, AGE calculates difference from current date/time

If you give two timestamps, AGE returns the difference between them.

If you give only one timestamp, AGE returns the difference between that timestamp and the current date/time.

Examples

This finds the difference between June 1, 2024, and June 1, 2020.

PostgreSQL

SELECT AGE('2024-06-01', '2020-06-01');

This finds the difference between the current date/time and June 1, 2024.

PostgreSQL

SELECT AGE('2024-06-01');

This finds the difference including time between two timestamps.

PostgreSQL

SELECT AGE(TIMESTAMP '2024-06-01 12:00:00', TIMESTAMP '2023-01-01 08:30:00');

Sample Program

This query calculates the age difference between June 1, 2024, and June 1, 2020.

PostgreSQL

SELECT AGE('2024-06-01', '2020-06-01') AS difference;

Important Notes

The result shows years, months, and days separately for easy reading.

AGE returns an interval type, which you can use in other calculations if needed.

If you swap the two dates, the result will be negative, showing the reverse difference.

Summary

AGE calculates the time difference between two dates or timestamps.

It returns the difference in years, months, and days as an interval.

You can use it with one or two timestamps depending on your need.

Practice

1. What does the PostgreSQL AGE function return when given two timestamps?

easy

A. The number of seconds between the two timestamps as an integer

B. The difference between the two timestamps as an interval showing years, months, and days

C. The sum of the two timestamps as a new timestamp

D. The earlier of the two timestamps

Solution

1. Step 1: Understand the AGE function purpose

   The AGE function calculates the time difference between two timestamps.

2. Step 2: Identify the output format

   It returns the difference as an interval showing years, months, and days.

3. Final Answer:

   The difference between the two timestamps as an interval showing years, months, and days -> Option B

4. Quick Check:

   AGE returns interval difference [OK]

Hint: AGE shows difference as years, months, days interval [OK]

Common Mistakes:

• Thinking AGE returns seconds or integer
• Confusing AGE with addition or subtraction of timestamps
• Assuming AGE returns a timestamp

2. Which of the following is the correct syntax to get the age difference between two timestamps '2023-01-01' and '2024-06-01' in PostgreSQL?

easy

A. SELECT AGE('2024-06-01', '2023-01-01');

B. SELECT AGE('2023-01-01', '2024-06-01');

C. SELECT AGE('2024-06-01'::timestamp '2023-01-01'::timestamp);

D. SELECT AGE('2023-01-01'::timestamp, '2024-06-01'::timestamp);

Solution

1. Step 1: Check AGE function parameter order

   AGE calculates the difference as first timestamp minus second timestamp, so the later date should come first.

2. Step 2: Identify correct syntax with proper order

   Using AGE('2024-06-01', '2023-01-01') returns the positive interval difference.

3. Final Answer:

   SELECT AGE('2024-06-01', '2023-01-01'); -> Option A

4. Quick Check:

   Later date first in AGE [OK]

Hint: Put later date first in AGE function [OK]

Common Mistakes:

• Reversing the order of timestamps
• Not casting strings to timestamps when needed
• Using AGE with only one parameter incorrectly

3. What is the output of this query?

SELECT AGE('2024-06-01'::date, '2023-01-01'::date);

medium

A. 1 year 5 mons 1 day

B. 1 year 6 mons 0 days

C. 1 year 4 mons 30 days

D. 1 year 5 mons 0 days

Solution

1. Step 1: Calculate difference between dates

   From 2023-01-01 to 2024-06-01 is 1 year and 5 months exactly.

2. Step 2: Understand AGE output format

   AGE returns interval as years, months, and days; days are zero here.

3. Final Answer:

   1 year 5 mons 0 days -> Option D

4. Quick Check:

   AGE returns 1 year 5 mons 0 days [OK]

Hint: Count full years and months between dates [OK]

Common Mistakes:

• Counting months incorrectly as 6 instead of 5
• Confusing days count
• Assuming AGE returns total days only

4. Identify the error in this query:

SELECT AGE('2023-01-01');

medium

A. Incorrect date format used

B. AGE function cannot accept a single argument

C. No error; AGE accepts a single argument

D. AGE requires casting to timestamp explicitly

Solution

1. Step 1: Check AGE function argument requirements

   AGE can accept one or two arguments; with one argument it returns difference from current date.

2. Step 2: Analyze the query

   The query uses one argument but does not cast it; however, AGE accepts one argument as timestamp or date.

3. Step 3: Identify actual error

   The query is valid; PostgreSQL implicitly handles the date string and computes age to current timestamp. No error.

4. Final Answer:

   No error; AGE accepts a single argument -> Option C

5. Quick Check:

   AGE needs two timestamps or one with current date [OK]

Hint: AGE with one argument uses current date [OK]

Common Mistakes:

• Assuming AGE always needs two arguments
• Thinking date format is wrong
• Believing casting is mandatory

5. You want to find the exact age difference between a person's birthdate '1990-04-15' and today, but only in years ignoring months and days. Which query correctly uses AGE and extracts only the years part?

hard

A. SELECT EXTRACT(YEAR FROM AGE(CURRENT_DATE, '1990-04-15'));

B. SELECT EXTRACT(YEAR FROM AGE('1990-04-15', CURRENT_DATE));

C. SELECT AGE(CURRENT_DATE, '1990-04-15')::year;

D. SELECT DATE_PART('year', AGE('1990-04-15', CURRENT_DATE));

Solution

1. Step 1: Use AGE with current date and birthdate

   AGE(CURRENT_DATE, '1990-04-15') returns interval from birthdate to today.

2. Step 2: Extract only the year part

   Use EXTRACT(YEAR FROM interval) to get full years ignoring months and days.

3. Final Answer:

   SELECT EXTRACT(YEAR FROM AGE(CURRENT_DATE, '1990-04-15')); -> Option A

4. Quick Check:

   EXTRACT YEAR from AGE with later date first [OK]

Hint: Use EXTRACT(YEAR FROM AGE(later, earlier)) [OK]

Common Mistakes:

• Reversing AGE argument order
• Using wrong function like DATE_PART with reversed arguments
• Trying to cast interval directly to year