Date and time types in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the DATE data type in MySQL?

The DATE data type stores date values in the format 'YYYY-MM-DD', representing year, month, and day without time information.

intermediate

How does the DATETIME type differ from the TIMESTAMP type in MySQL?

DATETIME stores date and time without timezone conversion, while TIMESTAMP stores date and time as UTC and converts to the current timezone on retrieval.

beginner

What is the format of the TIME data type in MySQL?

TIME stores time values in the format 'HH:MM:SS', representing hours, minutes, and seconds.

intermediate

Which MySQL date/time type would you use to store only the year and month?

MySQL does not have a specific type for only year and month; you can use DATE and ignore the day or store as a string.

intermediate

What happens if you insert an invalid date like '2024-02-30' into a DATE column in MySQL?

MySQL will reject the invalid date or store '0000-00-00' depending on SQL mode settings, because '2024-02-30' is not a valid calendar date.

Which MySQL data type stores both date and time without timezone conversion?

A TIME

B DATE

C DATETIME

D TIMESTAMP

DATETIME stores date and time exactly as entered without timezone conversion.

What is the default format for the TIME data type in MySQL?

A MM-DD-YYYY

B YYYY-MM-DD

C YYYY-MM-DD HH:MM:SS

D HH:MM:SS

TIME stores time values in 'HH:MM:SS' format.

Which MySQL data type automatically converts stored time to UTC and back to local time on retrieval?

A TIMESTAMP

B TIME

C DATE

D DATETIME

TIMESTAMP stores values in UTC and converts to local time on retrieval.

If you want to store only a date without time, which MySQL type should you use?

A DATE

B TIME

C DATETIME

D TIMESTAMP

DATE stores only the date part without time.

What will MySQL do if you insert '2024-02-30' into a DATE column with strict mode enabled?

A Store '0000-00-00'

B Reject the insert with an error

C Store '2024-02-30' as is

D Automatically correct to '2024-02-29'

In strict mode, MySQL rejects invalid dates like '2024-02-30' with an error.

Explain the differences between DATE, DATETIME, and TIMESTAMP types in MySQL.

Think about what each type stores and how timezones are handled.

Describe how MySQL handles invalid dates when inserting into a DATE column.

Consider SQL mode settings and validation rules.

Practice

1. Which MySQL data type should you use to store only a date without time?

easy

A. DATE

B. DATETIME

C. TIME

D. TIMESTAMP

Solution

1. Step 1: Understand the data types

   DATE stores only the date (year, month, day). DATETIME and TIMESTAMP store date and time. TIME stores only time.

2. Step 2: Match the requirement

   Since we want to store only the date without time, DATE is the correct choice.

3. Final Answer:

   DATE -> Option A

4. Quick Check:

   Date only = DATE [OK]

Hint: Date only? Use DATE type [OK]

Common Mistakes:

• Choosing DATETIME when only date is needed
• Using TIME for date storage
• Confusing TIMESTAMP with DATE

2. Which of the following is the correct syntax to declare a column named start_time that stores only time in MySQL?

easy

A. start_time TIME;

B. start_time DATE;

C. start_time DATETIME;

D. start_time TIMESTAMP;

Solution

1. Step 1: Identify the correct data type for time only

   The TIME type stores only time values (hours, minutes, seconds).

2. Step 2: Check syntax correctness

   Declaring a column as start_time TIME; is valid syntax in MySQL.

3. Final Answer:

   start_time TIME; -> Option A

4. Quick Check:

   Time only column = TIME type [OK]

Hint: Use TIME type for time-only columns [OK]

Common Mistakes:

• Using DATE or DATETIME for time-only columns
• Missing semicolon in declaration
• Confusing TIMESTAMP with TIME

3. Given the table events with a column event_datetime DATETIME, what will the query SELECT DATE(event_datetime) FROM events WHERE event_datetime = '2024-06-15 14:30:00'; return?

medium

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

B. 2024-06-15

C. 14:30:00

D. Error: Invalid function

Solution

1. Step 1: Understand the DATE() function

   The DATE() function extracts only the date part (year-month-day) from a datetime value.

2. Step 2: Apply the function to the given datetime

   Applying DATE('2024-06-15 14:30:00') returns 2024-06-15.

3. Final Answer:

   2024-06-15 -> Option B

4. Quick Check:

   DATE() extracts date only [OK]

Hint: DATE() extracts date part from datetime [OK]

Common Mistakes:

• Expecting full datetime as output
• Confusing DATE() with TIME() function
• Thinking DATE() causes error

4. You wrote this query to insert a time value: INSERT INTO schedule (meeting_time) VALUES ('25:00:00'); but it gives an error. What is the problem?

medium

A. Using DATETIME instead of TIME column type

B. Missing quotes around time value

C. Time value exceeds valid hour range (0-23)

D. Incorrect table name

Solution

1. Step 1: Check the time value format

   Valid time values must have hours between 00 and 23. '25:00:00' has 25 hours, which is invalid.

2. Step 2: Understand MySQL time validation

   MySQL rejects time values outside the valid range, causing an error on insert.

3. Final Answer:

   Time value exceeds valid hour range (0-23) -> Option C

4. Quick Check:

   Hours must be 0-23 in TIME values [OK]

Hint: Hours in TIME must be 0-23 [OK]

Common Mistakes:

• Assuming 25 is valid hour
• Forgetting quotes around time
• Confusing column type with error cause

5. You want to store the exact moment a user logs in, including date and time, and also want automatic timezone conversion to UTC. Which MySQL data type should you use?

hard

A. DATETIME

B. DATE

C. TIME

D. TIMESTAMP

Solution

1. Step 1: Understand the data types and timezone behavior

   TIMESTAMP stores date and time and automatically converts values to UTC for storage and back to local time on retrieval. DATETIME stores date and time but does not handle timezone conversion.

2. Step 2: Match requirement for timezone conversion

   Since automatic timezone conversion is needed, TIMESTAMP is the correct choice.

3. Final Answer:

   TIMESTAMP -> Option D

4. Quick Check:

   TIMESTAMP handles timezone conversion [OK]

Hint: Use TIMESTAMP for timezone-aware datetime [OK]

Common Mistakes:

• Choosing DATETIME and expecting timezone conversion
• Using DATE or TIME for full datetime
• Ignoring timezone needs