MySQL DATETIME vs TIMESTAMP Differences

This article explains how MySQL handles date and time functions when utilizing the DATETIME and TIMESTAMP data types. It covers the core differences in time zone handling, storage requirements, supported ranges, and how MySQL functions and queries interact with each data type to help you make the best choice for your database schema.

Time Zone Handling and Conversions

The primary difference in how MySQL processes these two data types lies in time zone conversion:

• TIMESTAMP: When you insert a value into a TIMESTAMP column, MySQL converts the value from the current session time zone to Coordinated Universal Time (UTC) for storage. When you query a TIMESTAMP column, MySQL converts the stored UTC value back to the current session’s time zone. This means if your database clients are in different time zones, they will see different local times for the same stored TIMESTAMP record.
• DATETIME: MySQL stores DATETIME values exactly as entered, without any time zone conversion. What you insert is exactly what you get back, regardless of the session time zone.

Because of this difference, functions like NOW() or CURRENT_TIMESTAMP behave differently depending on the target data type. When assigning NOW() to a TIMESTAMP column, it automatically adjusts based on the active time zone. When assigned to a DATETIME column, it stores the current local time of the server as a static string representation.

Supported Ranges and Storage

The range of dates each data type can handle dictates which functions and queries will succeed:

• TIMESTAMP: Supports a range of '1970-01-01 00:00:01' UTC to '2038-01-19 03:14:07' UTC. Values outside this range will fail or be truncated, which can cause errors when using date arithmetic functions (like DATE_ADD() or INTERVAL) that push the value past the year 2038.
• DATETIME: Supports a much wider range, from '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. Date functions operating on DATETIME columns are much less likely to encounter out-of-range errors.

In modern MySQL versions (5.6.4 and later), DATETIME requires 5 bytes of storage (plus additional bytes for fractional seconds), while TIMESTAMP requires 4 bytes (plus additional bytes for fractional seconds).

Behavior of Date and Time Functions

When using MySQL functions, the database engine treats DATETIME and TIMESTAMP differently during evaluation:

1. Implicit Type Conversion in Comparisons

If you compare a DATETIME column with a TIMESTAMP column, MySQL performs an implicit conversion. The TIMESTAMP value is converted to a DATETIME representation based on the current session time zone before the comparison occurs. This conversion step can occasionally prevent MySQL from utilizing indexes efficiently, leading to slower query performance.

2. The CONVERT_TZ() Function

The CONVERT_TZ(dt, from_tz, to_tz) function converts a datetime value from one time zone to another. * Using CONVERT_TZ() on a DATETIME column requires you to explicitly define the source and target time zones. * Using it on a TIMESTAMP is often redundant and can lead to unexpected double-conversions, because MySQL already translates TIMESTAMP values based on the session’s time_zone system variable.

3. Automatic Initialization and Updates

Both data types support automatic initialization to the current timestamp using DEFAULT CURRENT_TIMESTAMP and automatic updates using ON UPDATE CURRENT_TIMESTAMP. However, older MySQL versions only supported this behavior for TIMESTAMP columns. In modern MySQL, both types handle these automatic properties identically.