MySQL DATETIME vs TIMESTAMP: Complete Guide

MySQL DATETIME and TIMESTAMP data types serve different purposes despite both storing date and time information. DATETIME is better for storing specific, static date values like historical events or user birthdates, while TIMESTAMP excels at tracking record changes and handling time zone conversions automatically, making it ideal for applications that need consistent time tracking across different server environments.

Contents

• Key Differences Overview
• Range and Storage Requirements
• Time Zone Behavior
• Automatic Updates and Record Tracking
• PHP Application Considerations
• When to Use DATETIME
• When to Use TIMESTAMP

Key Differences Overview

The fundamental distinction between DATETIME and TIMESTAMP lies in their behavior with time zones and automatic updates. As PlanetScale explains, the DATETIME column does absolutely nothing concerning timezones - if you write a value of 2029-02-14 08:47 into the database, you will always and forever receive exactly that value. In contrast, TIMESTAMP automatically converts between time zones, storing values in UTC but presenting them in the server’s current time zone.

Another critical difference is the range support. According to CodeProject, DATETIME supports dates from ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’, making it suitable for historical records, while TIMESTAMP is limited to ‘1970-01-01 00:00:01’ UTC to ‘2038-01-09 03:14:07’ UTC, which restricts its use for dates before 1970 or after 2038.

Range and Storage Requirements

Supported Date Ranges

Storage Requirements

• DATETIME: Typically requires 8 bytes of storage
• TIMESTAMP:
  • Prior to MySQL 5.6.4: 4 bytes (+3 bytes for fractional seconds)
  • MySQL 5.6.4 and later: 4 bytes for fractional seconds support

The official MySQL documentation notes that this storage difference makes TIMESTAMP more efficient for applications with many timestamp fields, though the 2038 limitation should be considered for long-term applications.

Time Zone Behavior

DATETIME Time Zone Handling

DATETIME stores exactly what you insert, with no time zone conversion. This makes it ideal for applications where you need to preserve the exact moment as it was originally recorded.

The DATETIME column does absolutely nothing concerning timezones. If you write a value of 2029-02-14 08:47 into the database, you will always and forever receive a value of 2029-02-14 08:47.
— PlanetScale

TIMESTAMP Time Zone Handling

TIMESTAMP automatically handles time zone conversions, which can be both an advantage and a challenge:

MySQL automatically converts TIMESTAMP values from the current time zone to UTC for storage, and back to the current time zone for retrieval.
— PingCap

This behavior means:

• When you insert a TIMESTAMP value, MySQL converts it to UTC for storage
• When you retrieve it, MySQL converts it back to the current session’s time zone
• Changes to the server’s time zone settings can affect how TIMESTAMP values appear

For PHP applications, this means if your server’s time zone changes, TIMESTAMP values might display differently, potentially causing confusion if not handled carefully.

Automatic Updates and Record Tracking

TIMESTAMP Automatic Updates

One of TIMESTAMP’s most powerful features is its ability to automatically update when a record is modified:

TIMESTAMP used to track changes of records, and update every time when the record is changed.
— dbrnd

You can configure TIMESTAMP columns to automatically update on row modification:

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

DATETIME Static Storage

DATETIME columns remain static once set. If you want to track when a record was last modified, you need to manually update the DATETIME column in your PHP application:

// PHP code to manually update DATETIME
$updateQuery = "UPDATE users SET last_modified = NOW() WHERE id = ?";
$stmt = $pdo->prepare($updateQuery);
$stmt->execute([$userId]);

PHP Application Considerations

Server Environment Consistency

For PHP applications running on multiple servers or in different environments, TIMESTAMP provides better consistency because it stores everything in UTC and converts based on the server’s time zone settings. This ensures that:

• All servers see the same relative time for events
• Daylight saving time changes don’t affect stored values
• Time zone migrations are handled automatically

Date Handling in PHP

When working with DATETIME in PHP:

// DATETIME - straightforward handling
$datetime = '2024-01-15 14:30:00';
$phpDateTime = new DateTime($datetime);
echo $phpDateTime->format('Y-m-d H:i:s'); // Output: 2024-01-15 14:30:00

When working with TIMESTAMP in PHP:

// TIMESTAMP - consider time zone handling
$timestamp = '2024-01-15 14:30:00';
$phpDateTime = new DateTime($timestamp, new DateTimeZone('UTC'));
$phpDateTime->setTimezone(new DateTimeZone('America/New_York'));
echo $phpDateTime->format('Y-m-d H:i:s'); // Output depends on conversion

Database Connection Time Zone Settings

For TIMESTAMP to work correctly in PHP applications, ensure your database connection uses the appropriate time zone:

// PHP PDO connection with time zone
$pdo = new PDO("mysql:host=localhost;dbname=myapp;charset=utf8mb4", $username, $password);
$pdo->exec("SET time_zone = '+00:00'"); // Set to UTC for consistent TIMESTAMP behavior

When to Use DATETIME

DATETIME is the better choice for:

1. Historical Data: When you need to store dates before 1970 or after 2038
2. Specific Events: Birthdates, anniversaries, or events that should remain exactly as entered
3. User-Entered Values: When users expect to see exactly what they entered
4. Applications with Static Time References: Scheduling systems, calendars, or any application where the exact moment matters more than relative timing

Example use cases:

-- User profile data
CREATE TABLE users (
    id INT PRIMARY KEY,
    birth_date DATETIME,
    wedding_anniversary DATETIME
);

-- Event scheduling
CREATE TABLE events (
    id INT PRIMARY KEY,
    event_start DATETIME,
    event_end DATETIME
);

When to Use TIMESTAMP

TIMESTAMP is ideal for:

1. Record Tracking: Created_at and updated_at columns that need to track when records change
2. Multi-Server Applications: Consistent time tracking across different server environments
3. Audit Trails: Applications where you need to know when actions occurred
4. Applications with Time Zone Awareness: When users are in different time zones than the server

Example use cases:

-- Audit tracking
CREATE TABLE audit_logs (
    id INT PRIMARY KEY,
    user_action VARCHAR(100),
    action_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- User sessions
CREATE TABLE user_sessions (
    id INT PRIMARY KEY,
    user_id INT,
    login_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    last_activity TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

Conclusion

Key Takeaways

1. Range Considerations: Use DATETIME for historical dates (before 1970) or future dates beyond 2038; use TIMESTAMP for dates within the Unix epoch range.

2. Time Zone Handling: Choose DATETIME when you need exact, unmodified time values; choose TIMESTAMP when automatic time zone conversion is beneficial for your application.

3. Storage Efficiency: TIMESTAMP uses less storage (4 bytes vs 8 bytes) but comes with the 2038 limitation.

4. Automatic Updates: TIMESTAMP can automatically update when records are modified, while DATETIME requires manual updates.

Recommendations for PHP Applications

For most PHP applications, I recommend using TIMESTAMP for tracking record changes (created_at, updated_at) and DATETIME for user-specific dates (birthdates, event times). This combination gives you the benefits of automatic time zone handling for system tracking while preserving exact values for user-entered data.

Always consider your application’s longevity - if your application needs to store dates beyond 2038, DATETIME becomes the necessary choice despite its larger storage footprint.

Final Decision Framework

Ask yourself:

• Does this value need to track when something happened relative to now? → Use TIMESTAMP
• Does this value need to preserve the exact moment as originally entered? → Use DATETIME
• Will this date be before 1970 or after 2038? → Use DATETIME
• Are users in different time zones than the server? → Consider TIMESTAMP

Sources

1. Should I use the datetime or timestamp data type in MySQL? - Stack Overflow
2. Datetimes versus timestamps in MySQL — PlanetScale
3. Choosing the Right MySQL Time Type: Datetime vs. Timestamp - PingCap
4. DATETIME vs TIMESTAMP Data Type in MySQL? - GeeksforGeeks
5. MySQL: DATETIME vs TIMESTAMP - CodeProject
6. What is the difference between MySQL DATETIME and TIMESTAMP data type? - Tutorialspoint
7. What is the difference between DATETIME and TIMESTAMP data type in MySQL? - DEV Community
8. Difference Between MySQL DATETIME And TIMESTAMP DataTypes - C# Corner
9. What is the key difference between datetime and timestamp in MySQL - dbrnd