DATE_FORMAT and EXTRACT in SQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this DATE_FORMAT query?

Given a table events with a column event_date of type DATE, what is the output of the following query?

SELECT DATE_FORMAT(event_date, '%Y-%m-%d') AS formatted_date FROM events WHERE event_id = 1;

SQL

SELECT DATE_FORMAT(event_date, '%Y-%m-%d') AS formatted_date FROM events WHERE event_id = 1;

A '2023/15/07'

B '07/15/2023'

C '15-07-2023'

D '2023-07-15'

💡 Hint

The format string '%Y-%m-%d' means year-month-day with dashes.

DATE_FORMAT formats the date according to the pattern. '%Y' is 4-digit year, '%m' is 2-digit month, '%d' is 2-digit day, separated by dashes.

❓ query_result

intermediate

What does EXTRACT return for this date?

Consider the query:

SELECT EXTRACT(MONTH FROM '2024-02-29'::DATE) AS month_value;

What is the value of month_value?

SQL

SELECT EXTRACT(MONTH FROM '2024-02-29'::DATE) AS month_value;

A 2

B 29

C 2024

D NULL

💡 Hint

EXTRACT(MONTH FROM date) returns the month number from the date.

The date is February 29, 2024. EXTRACT(MONTH FROM date) returns 2 because February is the second month.

📝 Syntax

advanced

Which query correctly extracts the year from a timestamp?

You want to extract the year from a timestamp column named created_at. Which of the following queries is syntactically correct and returns the year as an integer?

A SELECT EXTRACT('YEAR' FROM created_at) FROM orders;

B SELECT EXTRACT(YEAR FROM created_at) FROM orders;

C SELECT EXTRACT(YEAR, created_at) FROM orders;

D SELECT EXTRACT(created_at, YEAR) FROM orders;

💡 Hint

EXTRACT uses the syntax EXTRACT(field FROM source). The field is not a string.

Option B uses the correct syntax: EXTRACT(YEAR FROM created_at). Options A, C, and D are invalid syntax.

❓ optimization

advanced

Optimizing date filtering with EXTRACT vs DATE_FORMAT

You want to select all rows from sales where the sale happened in March 2023. Which query is more efficient and why?

A SELECT * FROM sales WHERE EXTRACT(YEAR FROM sale_date) = 2023 AND EXTRACT(MONTH FROM sale_date) = 3;

B SELECT * FROM sales WHERE DATE_FORMAT(sale_date, '%Y-%m') = '2023-03';

C SELECT * FROM sales WHERE sale_date >= '2023-03-01' AND sale_date < '2023-04-01';

D SELECT * FROM sales WHERE sale_date LIKE '2023-03%';

💡 Hint

Filtering by range on the raw date column can use indexes better than functions on the column.

Option C uses a range condition on the raw date column, which can use indexes efficiently. Options B and C apply functions on the column, preventing index use. Option C uses LIKE which is less efficient and may not use indexes.

🔧 Debug

expert

Why does this EXTRACT query raise an error?

Given the query:

SELECT EXTRACT(QUARTER FROM '2023-05-10');

It raises an error. What is the cause?

SQL

SELECT EXTRACT(QUARTER FROM '2023-05-10');

A The date literal is missing a type cast to DATE or TIMESTAMP.

B The EXTRACT function requires the date to be in ISO format.

C QUARTER is not a valid field for EXTRACT in SQL.

D The FROM keyword is not allowed in EXTRACT.

💡 Hint

Check if the string literal is recognized as a date type by the database.

The string '2023-05-10' is a plain string literal. EXTRACT expects a date or timestamp type. Without casting, it causes a type error.

Practice

1. What does the SQL function EXTRACT(MONTH FROM '2024-06-15') return?

easy

A. '2024-06-15'

B. 15

C. 2024

D. 6

Solution

1. Step 1: Understand EXTRACT function

   The EXTRACT function pulls out a specific part of a date, here the MONTH part.

2. Step 2: Apply EXTRACT to the date

   From the date '2024-06-15', the month is 6 (June).

3. Final Answer:

   6 -> Option D

4. Quick Check:

   EXTRACT(MONTH FROM date) = 6 [OK]

Hint: EXTRACT pulls one date part, like month or year [OK]

Common Mistakes:

• Confusing day with month
• Expecting full date instead of part
• Using wrong syntax for EXTRACT

2. Which of the following is the correct syntax to get the year from a date using EXTRACT in SQL?

easy

A. EXTRACT(YEAR FROM '2024-06-15')

B. EXTRACT YEAR FROM '2024-06-15'

C. EXTRACT('YEAR', '2024-06-15')

D. EXTRACT('2024-06-15' FROM YEAR)

Solution

1. Step 1: Recall EXTRACT syntax

   The correct syntax is EXTRACT(part FROM date), with parentheses and FROM keyword.

2. Step 2: Check each option

   EXTRACT(YEAR FROM '2024-06-15') matches the correct syntax: EXTRACT(YEAR FROM '2024-06-15'). Others miss parentheses or have wrong order.

3. Final Answer:

   EXTRACT(YEAR FROM '2024-06-15') -> Option A

4. Quick Check:

   Correct EXTRACT syntax uses parentheses and FROM [OK]

Hint: EXTRACT needs parentheses and FROM keyword [OK]

Common Mistakes:

• Omitting parentheses
• Swapping arguments order
• Using quotes around part name

3. What is the output of this SQL query?

SELECT DATE_FORMAT('2024-06-15', '%Y-%m-%d'), EXTRACT(DAY FROM '2024-06-15');

medium

A. 2024-06-15, 6

B. 2024-06-15, 15

C. 2024/06/15, 15

D. 06-15-2024, 15

Solution

1. Step 1: Understand DATE_FORMAT with '%Y-%m-%d'

   This format outputs year-month-day as '2024-06-15'.

2. Step 2: Understand EXTRACT(DAY FROM date)

   Extracting DAY from '2024-06-15' gives 15.

3. Final Answer:

   2024-06-15, 15 -> Option B

4. Quick Check:

   DATE_FORMAT + EXTRACT day = '2024-06-15', 15 [OK]

Hint: DATE_FORMAT '%Y-%m-%d' matches original date format [OK]

Common Mistakes:

• Mixing month and day order
• Wrong format string in DATE_FORMAT
• Extracting wrong date part

4. Identify the error in this SQL query:

SELECT DATE_FORMAT('2024-06-15', '%Y-%d-%m');

medium

A. The date string must be in MM-DD-YYYY format

B. DATE_FORMAT requires three arguments

C. The format string swaps day and month incorrectly

D. EXTRACT should be used instead of DATE_FORMAT

Solution

1. Step 1: Analyze the format string '%Y-%d-%m'

   This format prints year, then day, then month, which is unusual and likely a mistake.

2. Step 2: Understand common date format order

   Usually, month comes before day as '%Y-%m-%d'. Swapping day and month causes confusing output.

3. Final Answer:

   The format string swaps day and month incorrectly -> Option C

4. Quick Check:

   Correct order is year-month-day, not year-day-month [OK]

Hint: Check format order: month before day usually [OK]

Common Mistakes:

• Mixing day and month in format string
• Wrong number of arguments to DATE_FORMAT
• Confusing DATE_FORMAT with EXTRACT

5. You want to list all orders from a table orders showing only the year and month of the order date in format YYYY-MM. Which SQL query correctly does this?

hard

A. SELECT DATE_FORMAT(order_date, '%Y-%m') AS year_month FROM orders;

B. SELECT EXTRACT(YEAR_MONTH FROM order_date) AS year_month FROM orders;

C. SELECT DATE_FORMAT(order_date, '%Y-%d') AS year_month FROM orders;

D. SELECT EXTRACT(MONTH FROM order_date) AS year_month FROM orders;

Solution

1. Step 1: Understand DATE_FORMAT for year and month

   Using '%Y-%m' in DATE_FORMAT returns year and month as 'YYYY-MM'.

2. Step 2: Check other options

   SELECT EXTRACT(YEAR_MONTH FROM order_date) AS year_month FROM orders; is invalid syntax; EXTRACT does not support YEAR_MONTH. SELECT DATE_FORMAT(order_date, '%Y-%d') AS year_month FROM orders; uses day instead of month. SELECT EXTRACT(MONTH FROM order_date) AS year_month FROM orders; returns only month number, missing year.

3. Final Answer:

   SELECT DATE_FORMAT(order_date, '%Y-%m') AS year_month FROM orders; -> Option A

4. Quick Check:

   DATE_FORMAT with '%Y-%m' gives year-month [OK]

Hint: Use DATE_FORMAT with '%Y-%m' for year and month [OK]

Common Mistakes:

• Using EXTRACT with unsupported parts
• Mixing day and month in format
• Selecting only month without year