DATE_FORMAT function in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of DATE_FORMAT with mixed specifiers

What is the output of the following query?

SELECT DATE_FORMAT('2024-06-15 14:35:20', '%W, %M %d, %Y %r') AS formatted_date;

MySQL

SELECT DATE_FORMAT('2024-06-15 14:35:20', '%W, %M %d, %Y %r') AS formatted_date;

A Saturday, 06 15, 2024 02:35:20 PM

B Sunday, June 15, 2024 14:35:20

C Saturday, June 15, 2024 02:35:20 PM

D Saturday, June 15, 2024 14:35:20

💡 Hint

Remember %W gives weekday name and %r gives 12-hour time with AM/PM.

The date '2024-06-15' is a Saturday. %W returns full weekday name, %M full month name, %d day with leading zero, %Y full year, and %r 12-hour time with seconds and AM/PM.

🧠 Conceptual

intermediate

Understanding DATE_FORMAT specifiers

Which DATE_FORMAT specifier returns the abbreviated month name (e.g., 'Jun')?

A %b

B %M

C %W

D %m

💡 Hint

Look for the specifier that returns a short month name.

%b returns abbreviated month name like 'Jan', 'Feb', 'Jun'. %M returns full month name, %m returns month number with leading zero, %W returns full weekday name.

📝 Syntax

advanced

Identify the syntax error in DATE_FORMAT usage

Which option contains a syntax error in using DATE_FORMAT function?

MySQL

SELECT DATE_FORMAT('2024-06-15', '%Y-%m-%d') AS date1;

A SELECT DATE_FORMAT('2024-06-15', '%Y/%m/%d') AS date2;

B SELECT DATE_FORMAT('2024-06-15', '%d-%m-%Y') AS date3;

C SELECT DATE_FORMAT('2024-06-15', '%Y-%m-%d') AS date1;

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

💡 Hint

Check for missing quotes or parentheses.

Option D is missing the closing quote for the format string, causing a syntax error. All others are syntactically correct.

❓ optimization

advanced

Optimizing date formatting for performance

You want to display only the year and month from a large table's datetime column using DATE_FORMAT. Which query is the most efficient?

A SELECT DATE_FORMAT(datetime_col, '%Y-%m') FROM big_table;

B SELECT CONCAT(YEAR(datetime_col), '-', MONTH(datetime_col)) FROM big_table;

C SELECT LEFT(DATE_FORMAT(datetime_col, '%Y-%m-%d'), 7) FROM big_table;

D SELECT SUBSTRING(DATE_FORMAT(datetime_col, '%Y-%m-%d'), 1, 7) FROM big_table;

💡 Hint

Consider readability and function overhead.

Using DATE_FORMAT with '%Y-%m' directly extracts year and month in one step, which is clear and efficient. Options A, B, and D add extra function calls or string manipulation, which is less efficient.

🔧 Debug

expert

Debugging unexpected output from DATE_FORMAT

A developer runs:

SELECT DATE_FORMAT('2024-06-15 23:59:59', '%h:%i %p') AS time_12h;

But the output is '11:59 PM' as expected. They want to show '23:59 PM'. Which change will cause the output to show '23:59 PM'?

A Change '%i' to '%I' in the format string.

B Change '%h' to '%H' in the format string.

C Remove '%p' from the format string.

D Change '%p' to '%P' in the format string.

💡 Hint

%h is 12-hour format, %H is 24-hour format.

The specifier '%h' returns hour in 12-hour format (01..12). '%H' returns hour in 24-hour format (00..23). To get '23:59 PM' (though PM is redundant with 24-hour), changing '%h' to '%H' will show '23:59'. The '%p' will still show AM/PM but is not typical with 24-hour format.

Practice

1. What does the MySQL function DATE_FORMAT(date, format) do?

easy

A. It calculates the difference between two dates.

B. It converts a string to a date type.

C. It adds days to a date value.

D. It changes how a date or time is displayed using a specific pattern.

Solution

1. Step 1: Understand the function purpose

   The DATE_FORMAT function is used to display dates in a specific format by applying a pattern string.

2. Step 2: Compare options with function behavior

   Only It changes how a date or time is displayed using a specific pattern. correctly describes changing the display format of a date/time value.

3. Final Answer:

   It changes how a date or time is displayed using a specific pattern. -> Option D

4. Quick Check:

   DATE_FORMAT changes display format = A [OK]

Hint: DATE_FORMAT changes date display style, not date value [OK]

Common Mistakes:

• Confusing DATE_FORMAT with date arithmetic functions
• Thinking it converts strings to dates
• Assuming it calculates date differences

2. Which of the following is the correct syntax to format a date as 'Year-Month-Day' using DATE_FORMAT?

easy

A. DATE_FORMAT(date, '%Y-%m-%d')

B. DATE_FORMAT(date, 'YYYY-MM-DD')

C. DATE_FORMAT(date, '%y/%M/%d')

D. DATE_FORMAT(date, 'YY-MM-DD')

Solution

1. Step 1: Recall correct format specifiers

   In MySQL, '%Y' is 4-digit year, '%m' is 2-digit month, '%d' is 2-digit day.

2. Step 2: Check each option's format string

   Only DATE_FORMAT(date, '%Y-%m-%d') uses correct MySQL format specifiers and separators for 'Year-Month-Day'. Others use invalid or wrong specifiers.

3. Final Answer:

   DATE_FORMAT(date, '%Y-%m-%d') -> Option A

4. Quick Check:

   Use %Y-%m-%d for year-month-day [OK]

Hint: Use %Y for year, %m for month, %d for day in DATE_FORMAT [OK]

Common Mistakes:

• Using uppercase YYYY instead of %Y
• Mixing format codes from other languages
• Using wrong separators like slashes instead of dashes

3. Given the query:
SELECT DATE_FORMAT('2024-06-15 14:30:00', '%W, %M %d, %Y %r') AS formatted_date;
What is the expected output in the formatted_date column?

medium

A. Sun, Jun 15, 2024 02:30 PM

B. Saturday, June 15, 2024 02:30:00 PM

C. Saturday, June 15, 2024 14:30:00

D. 2024-06-15 14:30:00

Solution

1. Step 1: Understand each format specifier

   %W = full weekday name (Saturday), %M = full month name (June), %d = day (15), %Y = year (2024), %r = 12-hour time with seconds and AM/PM (02:30:00 PM).

2. Step 2: Apply format to given datetime

   The datetime '2024-06-15 14:30:00' is 2:30 PM in 12-hour format, so output matches Saturday, June 15, 2024 02:30:00 PM exactly.

3. Final Answer:

   Saturday, June 15, 2024 02:30:00 PM -> Option B

4. Quick Check:

   Full weekday, month, and 12-hour time = C [OK]

Hint: Remember %r gives 12-hour time with seconds and AM/PM [OK]

Common Mistakes:

• Confusing %r with 24-hour time %H:%i:%s
• Using abbreviated weekday (%a) instead of full (%W)
• Ignoring AM/PM in output

4. Identify the error in this query:
SELECT DATE_FORMAT('2024-06-15', '%Y-%m-%d %H:%i:%s') AS formatted_date;
What will happen when this query runs?

medium

A. It will return NULL because the input has no time part.

B. It will cause a syntax error due to wrong format specifiers.

C. It will return '2024-06-15 00:00:00' as the time defaults to midnight.

D. It will return only the date part ignoring the time format.

Solution

1. Step 1: Analyze input and format

   The input date '2024-06-15' has no time, but MySQL treats missing time as '00:00:00'. Format includes time specifiers %H:%i:%s.

2. Step 2: Predict output behavior

   MySQL fills missing time with zeros, so output will be '2024-06-15 00:00:00'. No syntax error occurs.

3. Final Answer:

   It will return '2024-06-15 00:00:00' as the time defaults to midnight. -> Option C

4. Quick Check:

   Missing time defaults to 00:00:00 in DATE_FORMAT [OK]

Hint: Missing time defaults to 00:00:00, no error [OK]

Common Mistakes:

• Expecting syntax error for valid format
• Assuming NULL output for missing time
• Ignoring default midnight time fill

5. You want to display a datetime column created_at as 'Day-Month-Year Hour:Minute AM/PM' in a report. Which DATE_FORMAT pattern correctly formats it as '15-Jun-2024 02:30 PM'?

hard

A. DATE_FORMAT(created_at, '%d-%b-%Y %h:%i %p')

B. DATE_FORMAT(created_at, '%d-%m-%Y %H:%i %p')

C. DATE_FORMAT(created_at, '%d-%M-%Y %h:%i %P')

D. DATE_FORMAT(created_at, '%d-%b-%Y %H:%i %p')

Solution

1. Step 1: Match each format code to desired output

   %d = day with leading zero (15), %b = abbreviated month name (Jun), %Y = 4-digit year (2024), %h = 12-hour hour (02), %i = minutes (30), %p = AM/PM uppercase.

2. Step 2: Check options for correct codes and case

   DATE_FORMAT(created_at, '%d-%b-%Y %h:%i %p') matches all codes correctly. DATE_FORMAT(created_at, '%d-%m-%Y %H:%i %p') uses %m (numeric month) instead of %b. DATE_FORMAT(created_at, '%d-%M-%Y %h:%i %P') uses %M (full month) and %P (invalid). DATE_FORMAT(created_at, '%d-%b-%Y %H:%i %p') uses %H (24-hour) instead of %h.

3. Final Answer:

   DATE_FORMAT(created_at, '%d-%b-%Y %h:%i %p') -> Option A

4. Quick Check:

   Use %b for short month, %h for 12-hour, %p for AM/PM [OK]

Hint: Use %b for short month, %h for 12-hour, %p for AM/PM [OK]

Common Mistakes:

• Using %m instead of %b for month name
• Using %H (24-hour) instead of %h (12-hour)
• Using %P which is invalid in MySQL