MySQL DATETIME Explained: Data Type, Range, and Best Practices

1. What Is MySQL DATETIME?

MySQL DATETIME is a data type used to store both date and time in a single field. Managing date and time values in a database is essential for many applications, such as logging and reservation systems. The DATETIME type stores a date and time together and supports a wide range of values. Its range is from '1000-01-01 00:00:00' to '9999-12-31 23:59:59', and it also supports fractional seconds.

2. Overview of MySQL Date and Time Data Types

2.1 Data Types for Handling Dates and Times

MySQL provides the following data types for working with dates and times:

• DATE: Stores a date (year, month, day). The range is '1000-01-01' to '9999-12-31'.
• TIME: Stores time only. The range is '-838:59:59' to '838:59:59'.
• DATETIME: Stores both date and time. The range is '1000-01-01 00:00:00' to '9999-12-31 23:59:59'.
• TIMESTAMP: Stores a UNIX timestamp. The range is '1970-01-01 00:00:01' to '2038-01-19 03:14:07'.

2.2 Differences Between DATETIME and TIMESTAMP

DATETIME and TIMESTAMP are similar, but they have the following differences:

• Time zone: DATETIME stores a fixed value that does not depend on time zones. In contrast, TIMESTAMP is converted to UTC when stored and converted to the server’s current time zone when retrieved. Because of this, DATETIME is suitable for time zone–independent date/time values (for example, event times), while TIMESTAMP is suitable for data tied to the server time zone, such as logs.
• Storage format: DATETIME is stored as-is, while TIMESTAMP is stored as a UNIX timestamp. As a result, TIMESTAMP values are affected by the server’s time zone settings when representing time.

3. How to Use DATETIME in MySQL

3.1 Creating a DATETIME Column

To create a column with the DATETIME type, use the following SQL syntax:

CREATE TABLE sample_table (
    event_time DATETIME
);

In this example, a DATETIME column named event_time is created in a table called sample_table.

3.2 Inserting DATETIME Values

MySQL DATETIME values can be inserted in various formats. The basic format is 'YYYY-MM-DD HH:MM:SS'. For example:

INSERT INTO sample_table (event_time) VALUES ('2024-09-16 14:30:00');

The following formats are also allowed:

• 'YY-MM-DD HH:MM:SS': A format that uses a 2-digit year.
• 'YYYYMMDDHHMMSS': A format without separators.

Example:

INSERT INTO sample_table (event_time) VALUES ('24-09-16 14:30:00');
INSERT INTO sample_table (event_time) VALUES (20240916143000);

Data inserted in these formats will be stored correctly. If the year is specified with two digits, '70-99' is converted to 1970-1999, and '00-69' is converted to 2000-2069.

3.3 Retrieving DATETIME Values

When retrieving DATETIME values, MySQL displays them in the default 'YYYY-MM-DD HH:MM:SS' format. For example:

SELECT event_time FROM sample_table;

This query displays the values in the DATETIME column using the standard format.

4. Working with Fractional Seconds

4.1 DATETIME Precision

In MySQL, DATETIME values can include fractional seconds. You can specify precision using the fsp option, which allows storing fractional seconds from 0 to 6 digits. For example, to create a column with 3 digits of fractional seconds:

CREATE TABLE precise_times (
    event_time DATETIME(3)
);

In this example, the event_time column can store fractional seconds up to 3 digits.

4.2 Inserting Values with Fractional Seconds

To insert a DATETIME value that includes fractional seconds, use the following:

INSERT INTO precise_times (event_time) VALUES ('2024-09-16 14:30:00.123');

This query stores the value including fractional seconds accurately. The fractional part is stored without being truncated, and the precision is preserved when retrieving the value.

5. Best Practices for DATETIME

5.1 Choosing Between DATETIME and TIMESTAMP

• When to use DATETIME: For fixed date/time values that do not depend on time zones (for example, event start times or reservation dates).
• When to use TIMESTAMP: For date/time data related to the server time zone (for example, record creation or update timestamps).

5.2 Time Zone Management

Because DATETIME does not store time zone information, your application must manage time zones separately. On the other hand, TIMESTAMP automatically accounts for the server time zone when storing and retrieving values, making it suitable for systems operating across different time zones worldwide.

6. Common Mistakes and How to Avoid Them

6.1 Zero Dates and Invalid Values

In MySQL, if you attempt to insert an invalid DATETIME value, a zero date like '0000-00-00 00:00:00' may be stored. Since this is generally not a valid date, you should validate input data to prevent invalid values from being inserted. Implementing validation that ensures the input follows the correct range and format can help prevent zero dates from being stored.

6.2 Misusing Precision

When specifying fractional second precision, using the wrong precision may produce unexpected results. Only set fractional second precision when necessary, and choose the fsp value carefully. For example, if your application does not require sub-second precision, you do not need to add fractional seconds to a DATETIME column.

7. Summary

In this article, we explained MySQL’s DATETIME type in detail. DATETIME is a very useful data type for storing both date and time, and it is suitable when you need to store values that should not be affected by time zones. By understanding the differences between DATETIME and TIMESTAMP, how time zones work, and how to use fractional seconds, you can manage date/time data more effectively in your database. In addition, knowing common mistakes and how to avoid them helps maintain data consistency and reliability.

8. Frequently Asked Questions (FAQ)

Q1: What is the main difference between DATETIME and TIMESTAMP?

DATETIME stores a fixed date and time that does not depend on time zones. For example, it is suitable for storing reservation dates or event times that should remain the same in any time zone. In contrast, TIMESTAMP is stored in UTC and converted to the server’s time zone when retrieved. It is suitable for date/time data that depends on the server time zone, such as logs.

Q2: How can I store fractional seconds with DATETIME?

You can set fractional second precision by specifying an fsp value when creating the DATETIME column. For example, DATETIME(3) stores fractional seconds up to 3 digits. Use a properly formatted value including fractional seconds when inserting, and it will be stored correctly.

Q3: Should I use DATETIME or TIMESTAMP?

It depends on your use case. Use DATETIME when you want to store a fixed date and time. Use TIMESTAMP for date/time data that is affected by the server time zone, such as record creation or update times. Since TIMESTAMP performs automatic time zone conversion, it is suitable when your system must operate across different time zones.