I've seen questions like this:
"Is there a way to know when (date and time) the last statement captured in ... was actually ran?"more than once in some discussions (and customer issues) related to Performance Schema. I've seen answers provided by my colleagues and me after some limited testing. I've also noticed statements that it may not be possible.

Indeed, examples of wall clock date and time in the output of queries from the performance_schema are rare (and usually come from tables in the information_schema.  sys.format_time() function converts time to a nice, human readable format, but it still remains relative - it is not a date and time when something recorded in performance_schema happened.

In this post I'd like to document the answer I've seen and …

Introduction Dealing with time zones is always challenging. As a rule of thumb, it’s much easier if all date/time values are stored in the UTC format, and, if necessary, dealing with time zone conversations in the UI only. This article is going to demonstrate how you can accomplish this task with JDBC and the awesome … Continue reading How to store date, time, and timestamps in UTC time zone with JDBC and Hibernate →

A question which would come sometimes to mind when starting with MySQL is whether I should use DATETIME or TIMESTAMP data type since both appear to store same date and time component.


Similarities between datetime and timestamp:
1. Values contain both date and time parts.
2. Format of retrieval and display is "YYYY-MM-DD HH:MM:SS".
3. Can include a trailing fractional seconds part in up to microseconds (6 digits) precision.
4. With the fractional part included, the format for these values is "YYYY-MM-DD HH:MM:SS[.fraction]".
5. Both the TIMESTAMP and (as of MySQL 5.6.5) DATETIME offer automatic initialization and updating to the current date and time.

But both differ in some ways as mentioned below:
…

It's usually a good practice to have two columns called date_created and date_updated in every table. One can always use it in application and it helps in debugging too as to when a record was created and last updated in various circumstances and contexts.




This responsibility can be given to MySQL to automatically assign current time values to these columns.

In MySQL 5.6 onwards, this can be done by setting the data type of the columns to be either date time or timestamp and creating date_created column with NOT NULL DEFAULT CURRENT_TIMESTAMP  schema and date_updated column with NOT NULL DEFAULT '0000-00-00 00:00:00' as schema with attribute ON UPDATE CURRENT_TIMESTAMP.

…

In this post, we’ll discuss how MySQL 5.7 handles the old temporal types during an upgrade.

MySQL changed the temporal types in MySQL 5.6.4, and it introduced a new feature: microseconds resolution in the TIME, TIMESTAMP and DATETIME types. Now these parameters can be set down to microsecond granularity. Obviously, this means format changes, but why is this important?

Are they converted automatically to the new format?

If we had tables in MySQL 5.5 that used TIME, TIMESTAMP or DATETIME are these fields are going to be converted to the new format when upgrading to 5.6? The answer is “NO.” Even if we …

I was a bit wrong in my previous post. MySQL 5.6 does allow you to supply a fsp with CURRENT_TIMESTAMP (thanks Roy).

mysql> SELECT CURRENT_TIMESTAMP,CURRENT_TIMESTAMP(6);
+---------------------+----------------------------+
| CURRENT_TIMESTAMP   | CURRENT_TIMESTAMP(6)       |
+---------------------+----------------------------+
| 2013-10-27 10:38:59 | 2013-10-27 10:38:59.182530 |
+---------------------+----------------------------+
1 row in set (0.00 sec)

It however feels a bit weird to me as the CURRENT_TIMESTAMP is often used without () and doesn't look like a function. So when I tried to use a CURRENT_TIMESTAMP with a fsp of 6 it was not behaving how I expected it to be:

mysql> CREATE TABLE t1 (ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP(6));
ERROR 1067 (42000): Invalid …

MySQL 5.6 includes support for microsecode timestamp resolution, which is a great new feature.

To get the current timestamp in MySQL 5.5 you could use NOW(), SYSDATE() or CURRENT_TIMESTAMP.

mysql_5.5> SELECT NOW(),SYSDATE(),CURRENT_TIMESTAMP;
+---------------------+---------------------+---------------------+
| NOW()               | SYSDATE()           | CURRENT_TIMESTAMP   |
+---------------------+---------------------+---------------------+
| 2013-10-26 15:46:24 | 2013-10-26 15:46:24 | 2013-10-26 15:46:24 |
+---------------------+---------------------+---------------------+
1 row in set (0.01 sec)

If we run the same statement in MySQL 5.6 the output is the same. This is great for compatibility, but what if we want those microsecond timestamps?

 …

MySQL 5.6 introduces a new feature – microseconds resolution in some temporal types. As of 5.6.4 TIME, TIMESTAMP and DATETIME can have a fractional part. To create a field with subseconds you can specify precision in brackets: TIME(3), DATETIME(6) etc.

Obviously, the new feature requires the format change. All three types may now have a tail with a fractional part. The tail may be one, two or three bytes long and can store up to six digits after the point.

The non-fractional part has changed too. Thus, DATETIME uses only five bytes comparing to eight in previous versions.

As of revision 79 the …

There are great features in MySQL 5.6. But not only that. We also tried to correct some old behaviors and limitations which, over the years, have shown to irritate our Community. The behavior of TIMESTAMP columns is one of them.

My colleague Martin Hansson did most of the work and summarized it well in his blog. Thanks to him, since MySQL 5.6.5, it's possible to declare more than one TIMESTAMP column with the DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP attributes. And it's possible to have DATETIME columns with such attributes. Two limitations lifted!

But that is not the end of the story. TIMESTAMP was still special. Unlike other datatypes, if not declared with the NULL or NOT NULL attributes, it would automatically get NOT NULL. And the first TIMESTAMP column of the table would automatically …

In the yet to be released MySQL 5.6.6 DMR, there has been a change to the restriction of just one TIMESTAMP column with the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP syntax. It is now possible for any TIMESTAMP to have either column defintion.

More information at http://dev.mysql.com/doc/refman/5.6/en/news-5-6-5.html