The safest way to save dates to the database in PHP is: 1. Select the appropriate data type (DATETIME is suitable for long-term storage, TIMESTAMP is suitable for automatic time zone conversion); 2. Use the DateTime class to process time and the unified format is 'Ymd H:i:s'; 3. Use UTC to unify the time zone and set the time zone when connecting to MySQL. Avoid storing timestamps directly or using irregular formats to ensure queries, sorting, and cross-language compatibility.

When saving dates to the database, the most secure way in PHP is actually just a few key points: using data types, handling time zones, and unified format specifications .

Commonly used date types in MySQL are DATE , DATETIME and TIMESTAMP . When operating in PHP, just be careful not to store time randomly as a string, and there will basically be no problems.

Store with DATETIME or TIMESTAMP type

These two are the most commonly used options:

• DATETIME : Can represent a larger range of time (1000 to 9999), suitable for long-term retention data
• TIMESTAMP : Automatically convert time zones, affected by MySQL configuration, with a smaller range (1970~2038)

If your system involves multiple time zones, or you want the database to automatically convert time zones for you, then TIMESTAMP is more suitable; otherwise, DATETIME is generally recommended, which is more stable and controllable.

Save the same format before, don't spell strings casually

In PHP, it is recommended to use DateTime class to handle time, so that errors are not prone to errors:

 $date = new DateTime();
$dateStr = $date->format('Ymd H:i:s'); // The standard format can be inserted directly into DATETIME

Don't use time() directly to get an integer stored in the database, which saves space but is not convenient for querying and sorting. Unless you have a special reason, it is most convenient to use the standard date format directly.

A common mistake is that someone writes it like this:

 $now = date('Y/m/d H:i:s'); // Used a slash, an error may be reported in some SQL occasions

Remember to have standard formats, use horizontal lines - and colon : , such as 'Ymd H:i:s' , which is the default recognized format by MySQL.

The time zone must be unified, don't mix it up

If the front-end users are distributed in different time zones, you need to decide:

• Is the local time or UTC saved?
• What time zone does the database store?

The general recommended practices are:

• Using UTC time unified storage in PHP
• When displayed to users, convert according to their time zone

You can set it like this:

 $dt = new DateTime('now', new DateTimeZone('UTC'));
// Insert the database and convert it into a string

At the same time, it is necessary to ensure that MySQL connections also use a unified time zone:

 SET time_zone = ' 00:00';

Or execute SQL to set the session time zone after the connection.

Small details are easily overlooked

• Field default value : can be set to CURRENT_TIMESTAMP , but be careful that it only takes effect on TIMESTAMP , DATETIME does not support it
• Automatic update time : ON UPDATE CURRENT_TIMESTAMP This function can only be used for TIMESTAMP , and there can only be one such field at most (old version of MySQL)
• Cross-language compatibility : If your project may read and write this field in other languages ??in the future, using standard formats and UTC time can reduce the hassle

Basically that's it. Choose the type, unified format, pay attention to the time zone, and the rest is to insert and update normally.

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