AGE function for differences in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the age difference between two dates using the AGE function.

PostgreSQL

SELECT AGE([1], '2023-01-01') AS difference;

Drag options to blanks, or click blank then click option'

A'2021-01-01'

B'2024-01-01'

C'2023-12-31'

D'2022-01-01'

Attempts:

3 left

💡 Hint

Common Mistakes

Using an earlier date as the first argument results in a negative interval.

Forgetting to put the dates in quotes.

The AGE function calculates the interval between two dates. Here, the first argument should be a later date to get a positive difference.

2fill in blank

medium

Complete the code to calculate the age difference between the current date and a given birthdate.

PostgreSQL

SELECT AGE(CURRENT_DATE, [1]) AS age;

Drag options to blanks, or click blank then click option'

A'1999-12-31'

B'2025-05-15'

C'2000-05-15'

D'2023-12-31'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a future date as birthdate.

Not using CURRENT_DATE for the current date.

The AGE function here calculates the age from the birthdate to today. The birthdate must be in the past.

3fill in blank

hard

Fix the error in the code to correctly calculate the age difference between two timestamps.

PostgreSQL

SELECT AGE([1], '2023-06-01 12:00:00') AS diff;

Drag options to blanks, or click blank then click option'

A'2023-05-31 12:00:00'

B'2023-06-02 12:00:00'

C'2023-06-01 11:00:00'

D'2023-06-01 13:00:00'

Attempts:

3 left

💡 Hint

Common Mistakes

Using an earlier timestamp as the first argument causes negative intervals.

Not including time in the timestamp string.

The AGE function returns the interval between the first and second timestamp. To get a positive difference, the first timestamp should be later.

4fill in blank

hard

Fill both blanks to calculate the age difference between two dates and filter results where the difference is more than 1 year.

PostgreSQL

SELECT AGE([1], [2]) AS age_diff FROM events WHERE AGE([1], [2]) > INTERVAL '1 year';

Drag options to blanks, or click blank then click option'

A'2020-01-01'

B'2019-12-31'

C'2021-01-01'

D'2022-01-01'

Attempts:

3 left

💡 Hint

Common Mistakes

Using dates less than a year apart.

Swapping the dates causing negative intervals.

The AGE function calculates the interval between the two dates. Filtering for intervals greater than 1 year requires the dates to be at least one year apart.

5fill in blank

hard

Fill all three blanks to create a query that calculates the age difference between two timestamps, extracts the year part, and filters for differences of 5 years or more.

PostgreSQL

SELECT EXTRACT(year FROM AGE([1], [2])) AS years_diff FROM users WHERE EXTRACT(year FROM AGE([1], [2])) >= [3];

Drag options to blanks, or click blank then click option'

A'2015-06-01 08:00:00'

B'2010-06-01 08:00:00'

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping timestamps causing negative intervals.

Using a string instead of a number for the threshold.

Using the wrong EXTRACT field.

The AGE function calculates the interval between two timestamps. EXTRACT(year FROM ...) gets the year part of the interval. Filtering for differences of 5 years or more requires the threshold 5.

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