Should we use the datetime or timestamp data type in MySQL?

In MySQL, choosing between DATETIME and TIMESTAMP depends on your specific requirements for date range, time zone handling, and storage efficiency. Here’s a detailed comparison with examples:

1. Key Differences

Feature	DATETIME	TIMESTAMP
Date Range	1000-01-01 00:00:00 to 9999-12-31 23:59:59	1970-01-01 00:00:01 UTC to 2038-01-19 03:14:07 UTC
Storage	5–8 bytes (depending on precision)	4 bytes
Time Zone Handling	Stored as-is (no time zone conversion)	Converted to UTC for storage and back to the session time zone on retrieval.
Automatic Updates	No (unless explicitly configured)	Yes (with DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP)
Use Case	Historical/future dates, no time zone needs	Time-sensitive data, automatic timestamps, time zone awareness.

2. When to Use DATETIME

• Example: Storing a user’s birthdate or future event dates.
• Reasons:
  • Wider date range (supports dates beyond 2038).
  • No implicit time zone conversion.

Example Table:

sql

CREATE TABLE events (
    event_id INT PRIMARY KEY,
    event_name VARCHAR(50),
    event_time DATETIME  -- Stores time as literal value
);

INSERT INTO events (event_id, event_name, event_time)
VALUES (1, 'Concert', '2050-12-31 20:00:00');

3. When to Use TIMESTAMP

• Example: Tracking row creation/modification times or user login timestamps.
• Reasons:
  • Automatic time zone conversion (ideal for global apps).
  • Smaller storage footprint.
  • Built-in auto-update for auditing.

Example Table:

sql

CREATE TABLE user_actions (
    action_id INT PRIMARY KEY,
    user_id INT,
    action_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);

INSERT INTO user_actions (action_id, user_id) 
VALUES (1, 100);  -- action_time auto-populates with current UTC time

4. Time Zone Behavior Example

Assume the MySQL server’s time zone is set to UTC+0, and a client session uses UTC+8:

sql

-- Insert a TIMESTAMP and DATETIME value
INSERT INTO events (event_id, event_name, event_time)
VALUES (2, 'Meeting', '2023-10-01 12:00:00');

INSERT INTO user_actions (action_id, user_id)
VALUES (2, 101);  -- action_time = current UTC time (e.g., '2023-10-01 04:00:00 UTC')

Query Results:

sql

-- Client session time zone: UTC+8
SELECT event_time FROM events WHERE event_id = 2;
-- Output: '2023-10-01 12:00:00' (DATETIME remains literal)

SELECT action_time FROM user_actions WHERE action_id = 2;
-- Output: '2023-10-01 12:00:00' (TIMESTAMP converts UTC to client's UTC+8)

5. Summary of Recommendations

• Use DATETIME if:
  • You need dates outside 1970–2038.
  • Time zone conversion is irrelevant (e.g., birthdays, historical records).
• Use TIMESTAMP if:
  • You need automatic time zone handling.
  • Space efficiency matters (e.g., high-volume logging).
  • You want auto-updating fields for audit trails.

6. Edge Cases

• Year 2038 Problem: TIMESTAMP will fail for dates beyond 2038. Use DATETIME instead.
• Precision: Both support fractional seconds (e.g., DATETIME(6) for microseconds), but TIMESTAMP has a narrower range.

By aligning your choice with these criteria, you’ll optimize storage, functionality, and global compatibility.