The main difference between NOW() and CURRENT_TIMESTAMP() is in the usage scenario; CURRENT_TIMESTAMP can be used as a column default value and automatically update keywords, while NOW() is only a function; both return the same result in the query, but when defining the table structure, you must use CURRENT_TIMESTAMP to set the default value or automatically update the timestamp.
In MySQL, NOW() and CURRENT_TIMESTAMP() look similar and have similar functions, but there are still some nuances between them. If you just want to know the difference quickly, let’s talk about the key points first:
- Both can be used to obtain the current date and time;
-
NOW()is a function, andCURRENT_TIMESTAMP()is a keyword whose function is also a default value; - In some contexts (such as setting the default value of a column),
CURRENT_TIMESTAMPis more commonly used and recommended.
The following are some common usage scenarios.
1. Basic usage: Get the current time
The most basic function of these two functions is to return the current date and time, and the format is YYYY-MM-DD HH:MM:SS .
SELECT NOW(), CURRENT_TIMESTAMP();
The execution results are usually the same, all at the current point in time. But note that NOW() returns the time when the statement starts executing, not the time when the function is called . If NOW() is called multiple times in a long transaction, it will always return to the same point in time.
In contrast, CURRENT_TIMESTAMP() is actually synonymous with NOW() , and there is no difference in this query scenario.
2. Use as the default value of the column
This is where the two truly reflect the difference.
When you create a table and want a field to automatically record the insertion time, it is usually written like this:
CREATE TABLE example (
id INT PRIMARY KEY AUTO_INCREMENT,
created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);You can't write it as:
created_at TIMESTAMP DEFAULT NOW()
This will report an error. Because when defining the default value, MySQL only accepts CURRENT_TIMESTAMP form and does not support the NOW() function.
So in this scenario, CURRENT_TIMESTAMP must be used to be legal .
3. Automatically update the timestamp
In addition to the default value, MySQL also supports automatic update of timestamps when data is updated, and at this time, it also depends on CURRENT_TIMESTAMP .
CREATE TABLE example (
id INT PRIMARY KEY AUTO_INCREMENT,
updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);This definition means:
- When inserting a new record, the current time will be automatically filled in;
- When this record is updated, this field will also be automatically updated to the current time.
Similarly, ON UPDATE NOW() is not allowed, only CURRENT_TIMESTAMP can be used.
4. Small differences in time zone processing (advanced)
Although not encountered in most cases, NOW() and CURRENT_TIMESTAMP() are affected by the current connection time zone. For example, if you set the connection time zone to East Eight in the application, then the local time will be returned.
But if you deploy database services across time zones, or do replication and migration operations, you should pay attention to this point. However, the two behaviors in this regard are consistent and there is no need to be a special distinction.
In general, these two functions are interchangeable in the query, but when defining the table structure, especially the default value and automatic update, you must use CURRENT_TIMESTAMP .
Basically that's it.
The above is the detailed content of mysql now() vs current_timestamp(). For more information, please follow other related articles on the PHP Chinese website!
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