MySQL TIMESTAMP Explained: Time Zones, DATETIME Differences, and the 2038 Problem

1. What is MySQL TIMESTAMP?

The TIMESTAMP data type in MySQL is designed to store a specific point in time in UTC (Coordinated Universal Time) and automatically handle time zone conversion when saving and retrieving data. This data type can handle dates and times in the range from January 1, 1970 to January 19, 2038. When saving data to the database, TIMESTAMP uses the current time zone, and when retrieving data, it is automatically converted based on the system time zone.

Differences Between TIMESTAMP and DATETIME

The DATETIME data type is often compared with TIMESTAMP. DATETIME stores date and time values “as-is,” so the stored data is not affected by time zones. In contrast, TIMESTAMP is converted to UTC when stored and converted back to the system time zone when retrieved, which helps prevent time offsets across environments.

For example, TIMESTAMP is especially useful during system migrations or when working with databases across multiple time zones. DATETIME supports a wider range—from year 1000 to 9999—so it is often used to avoid the Year 2038 problem.

Example Usage of TIMESTAMP

You can create a table using TIMESTAMP as follows.

CREATE TABLE events (
    id INT AUTO_INCREMENT PRIMARY KEY,
    event_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

In this example, the event_time column automatically stores the current time when a record is inserted, and overwrites that value each time the record is updated.

2. Basic Usage of TIMESTAMP

When using TIMESTAMP in MySQL, it is important to understand the basic ways to insert and retrieve values. Below are several common approaches to working with TIMESTAMP data.

Insert a Date and Time

When inserting data into a TIMESTAMP column, you typically specify the date and time in a string format. The date is represented as “YYYY-MM-DD” and the time as “hh:mm:ss”.

INSERT INTO events (event_time) VALUES ('2023-10-01 12:30:00');

This SQL statement inserts 12:30:00 on October 1, 2023 into the event_time column.

Insert the Current Time

Using MySQL’s NOW() function, you can easily get the current date and time. This function returns the current date and time based on the system time zone, and you can insert it directly into a TIMESTAMP column.

INSERT INTO events (event_time) VALUES (NOW());

In this example, the current time at the moment the SQL is executed is inserted automatically.

Use the Auto-Update Feature

If you specify ON UPDATE CURRENT_TIMESTAMP for a TIMESTAMP column, the update time is automatically recorded every time the record is updated.

CREATE TABLE orders (
    id INT AUTO_INCREMENT PRIMARY KEY,
    order_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

In this table, order_time is set to the current time when the record is created, and it is updated every time the record is updated.

3. Working with TIMESTAMP and Time Zones

One of the biggest features of TIMESTAMP is time zone handling. Stored data is always converted to UTC, and when you retrieve it from the database, it is converted again to match the system time zone.

How to Check the Time Zone Setting

In MySQL, you can set the time zone per server or per session. You can check the time zone setting using the SHOW VARIABLES command.

SHOW VARIABLES LIKE 'time_zone';

This command returns the time zone currently configured for the database. To change the time zone, use the following statement.

SET time_zone = '+09:00';

Time Zone Differences Between TIMESTAMP and DATETIME

The DATETIME type stores date and time without considering time zones, while the TIMESTAMP type is converted to UTC when saved. Therefore, in environments where multiple time zones coexist, TIMESTAMP is often the better choice.

4. The Year 2038 Problem and Its Impact

The Year 2038 problem is caused by the limitation of the TIMESTAMP type on 32-bit systems. MySQL’s TIMESTAMP type is based on the number of seconds since 00:00:00 UTC on January 1, 1970. When it exceeds 03:14:07 UTC on January 19, 2038, this value overflows.

How to Avoid the Year 2038 Problem

To avoid this problem, it is recommended to use a 64-bit system or the wider-range DATETIME type. DATETIME can handle dates and times from year 1000 to 9999, so it can be used safely beyond 2038.

You can also avoid this issue by upgrading your system. Since 64-bit systems do not have the Year 2038 limitation, it is important to consider upgrading your database and applications.

5. Practical Use Cases for the TIMESTAMP Type

The MySQL TIMESTAMP type is not only used for storing basic date and time values, but also supports a variety of practical patterns such as automatically inserting or updating the current time. Here are some common advanced use cases.

Automatically Insert the Current Time

When defining a TIMESTAMP column, you can set CURRENT_TIMESTAMP as the default value so that the current date and time is automatically inserted whenever a new record is created. For example, to create a table that automatically records when an order occurs, you can do the following.

CREATE TABLE orders (
    id INT AUTO_INCREMENT PRIMARY KEY,
    order_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Automatically Record the Update Time

By specifying ON UPDATE CURRENT_TIMESTAMP, the update time is automatically recorded every time a record is updated. This makes it easy to manage update history automatically.

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50),
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

Using Multiple TIMESTAMP Columns

In MySQL, you can include multiple TIMESTAMP columns in a table, but by default only one column can have CURRENT_TIMESTAMP as its default value. If you want to manage multiple timestamps automatically, explicitly set values for the other columns or use the DATETIME type.

CREATE TABLE posts (
    id INT AUTO_INCREMENT PRIMARY KEY,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

6. Important Notes When Using the TIMESTAMP Type

When using the TIMESTAMP type, there are several important caveats to understand. Knowing these helps prevent unexpected inconsistencies and errors.

NULL Constraints and Default Values

By default, a NOT NULL constraint is applied to TIMESTAMP columns. In other words, if you want to allow NULL values, you must explicitly specify DEFAULT NULL.

CREATE TABLE logs (
    id INT AUTO_INCREMENT PRIMARY KEY,
    log_time TIMESTAMP DEFAULT NULL
);

You can also specify DEFAULT 0 to set an invalid datetime value of 0000-00-00 00:00:00 by default. However, this is not recommended. In MySQL’s strict SQL mode, this invalid datetime can cause errors.

The Problem with 0000-00-00 00:00:00

Some MySQL versions support 0000-00-00 00:00:00 as an invalid datetime value, but it can cause operational issues in real-world systems. In particular, systems that prioritize data integrity should avoid such invalid values. Instead, it is recommended to use NULL or an appropriate default value.

CREATE TABLE sessions (
    id INT AUTO_INCREMENT PRIMARY KEY,
    start_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    end_time TIMESTAMP NULL
);

Impact of the System Time Zone

Because the TIMESTAMP type is stored after conversion to UTC, you should be careful when migrating databases across different time zones. If the server time zone setting changes, the retrieved times may become unintended values. It’s important to manage time zones accurately.

SET time_zone = 'Asia/Tokyo';

This command sets the database time zone to Tokyo and ensures accurate management of conversions from UTC.

7. Summary and Recommendations

The TIMESTAMP type is a powerful tool for efficiently managing dates and times in MySQL. In particular, automatic conversion with time zones and automatic time recording on create/update are very convenient. However, it is important to understand limitations and caveats such as the Year 2038 problem and how NULL values are handled.

When to Use TIMESTAMP

• When you need auto-update behavior, TIMESTAMP is ideal—especially if you want to record a timestamp automatically every time a record is updated.
• In systems that must consider time zones, the UTC-based conversion behavior of TIMESTAMP is helpful.
• On the other hand, if you need future-proof range or must handle dates outside the supported range (after 2038), consider using DATETIME.

Finally, choose between TIMESTAMP and DATETIME based on your system requirements to ensure data integrity and maintainability.

8. Frequently Asked Questions (FAQ)

Questions and issues related to MySQL TIMESTAMP are common among developers, so this section summarizes frequently asked questions. These FAQs provide helpful tips and solutions for handling TIMESTAMP correctly.

How should I choose between TIMESTAMP and DATETIME?

TIMESTAMP automatically converts values based on time zones using UTC, so it is suitable for applications and systems that must account for multiple time zones. It also supports automatically saving date/time values when records are created or updated. In contrast, DATETIME stores values “as-is,” so it is better when you need consistent datetime management without time zone conversion.

Is it true that TIMESTAMP can’t be used after 2038?

Yes. The Year 2038 problem applies to the 32-bit TIMESTAMP type. Because it is based on the number of seconds since January 1, 1970, it cannot represent datetimes after January 19, 2038. To avoid this, migrating to a 64-bit system or using the DATETIME type is recommended.

How can I allow NULL values in a TIMESTAMP column?

To allow NULL values in a TIMESTAMP column, you must explicitly specify DEFAULT NULL as shown below.

CREATE TABLE logs (
    id INT AUTO_INCREMENT PRIMARY KEY,
    log_time TIMESTAMP DEFAULT NULL
);

With this setting, if you insert a record without specifying a datetime, a NULL value is stored.

If I change the time zone setting, will it affect existing TIMESTAMP data?

Because TIMESTAMP values are converted to UTC when stored, changing the time zone setting affects how the data is displayed when retrieved. The underlying data is still stored in UTC, but it will be converted based on the new time zone, which changes the retrieved time values. To keep data consistent, it’s important to standardize time zone settings across the system.

If I use CURRENT_TIMESTAMP, can I still insert a specific datetime?

CURRENT_TIMESTAMP automatically inserts the current time when the record is inserted, but you can still insert a specific datetime explicitly by using NOW() or a string literal.

INSERT INTO events (event_time) VALUES ('2023-10-01 12:30:00');

In this way, you can manually insert datetimes even when using CURRENT_TIMESTAMP.