time for standards 2

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 default value for 'ts'
mysql> CREATE TABLE t1 (ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP(0));
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO t1 VALUES(CURRENT_TIMESTAMP(6));
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM t1;
+---------------------+
| ts                  |
+---------------------+
| 2013-10-27 10:42:30 |
+---------------------+
1 row in set (0.00 sec)

So it didn't allow me to use a default of CURRENT_TIMESTAMP(6). It however accepted a CURRENT_TIMESTAMP with a fsp of 6, and then threw away the microseconds without any warning.
After some more investigating it turned out that there is a correct way of doing this:

mysql> CREATE TABLE t1 (ts TIMESTAMP(6) DEFAULT CURRENT_TIMESTAMP);
ERROR 1067 (42000): Invalid default value for 'ts'
mysql> CREATE TABLE t1 (ts TIMESTAMP(6) DEFAULT CURRENT_TIMESTAMP(6));
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO t1 VALUES(NULL);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM t1;
+----------------------------+
| ts                         |
+----------------------------+
| 2013-10-27 10:47:01.604891 |
+----------------------------+
1 row in set (0.00 sec)

So you must specify a fsp for the column time AND the default value, then it works.

time for standards

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> SELECT NOW(),SYSDATE(),CURRENT_TIMESTAMP;
+---------------------+---------------------+---------------------+
| NOW()               | SYSDATE()           | CURRENT_TIMESTAMP   |
+---------------------+---------------------+---------------------+
| 2013-10-26 15:47:21 | 2013-10-26 15:47:21 | 2013-10-26 15:47:21 |
+---------------------+---------------------+---------------------+
1 row in set (0.00 sec)

For the microsecond timestamps we have to specify the fsp or fractional seconds precision, which is an integer between 0 and 6.

mysql_5.6> SELECT NOW(6),SYSDATE(6),CURRENT_TIMESTAMP;
+----------------------------+----------------------------+---------------------+
| NOW(6)                     | SYSDATE(6)                 | CURRENT_TIMESTAMP   |
+----------------------------+----------------------------+---------------------+
| 2013-10-26 15:50:12.378787 | 2013-10-26 15:50:12.378892 | 2013-10-26 15:50:12 |
+----------------------------+----------------------------+---------------------+
1 row in set (0.00 sec)

Please note that you can't specify a fsp for CURRENT_TIMESTAMP.
So how do other databases behave?

PostgreSQL:

dveeden=# SELECT NOW(),CURRENT_TIMESTAMP;
              now              |              now              
-------------------------------+-------------------------------
 2013-10-26 15:55:11.548362+02 | 2013-10-26 15:55:11.548362+02
(1 row)

There is no SYSDATE() function in PostgreSQL (tested with 9.1). And you may not specify a fsp. And you get microseconds by default.

SQLite:

sqlite> select current_timestamp;
2013-10-26 13:57:57
sqlite> select strftime("%Y-%m-%d %H:%M:%f", "now"); 
2013-10-26 13:59:42.408

Version 3.7 doesn't have sysdate() or now(), only current_timestamp and no microseconds by default.

So it seems to be hard to write version and implementation tolerant SQL code. I couldn't easily find any information about what the SQL standards dictate.

There is one trick which could help in some situation:

mysql_5.5> SELECT NOW(/*!50604 6*/);
+---------------------+
| NOW()               |
+---------------------+
| 2013-10-26 16:04:04 |
+---------------------+
1 row in set (0.00 sec)

mysql_5.6> SELECT NOW(/*!50604 6*/);
+----------------------------+
| NOW( 6 )                   |
+----------------------------+
| 2013-10-26 16:03:37.136133 |
+----------------------------+
1 row in set (0.01 sec)

Another thrick you might think of is changing the date_time_format and time_format.

mysql_5.6> show global variables like '%time_format';
+-----------------+-------------------+
| Variable_name   | Value             |
+-----------------+-------------------+
| datetime_format | %Y-%m-%d %H:%i:%s |
| time_format     | %H:%i:%s          |
+-----------------+-------------------+
2 rows in set (0.00 sec)

But that won't work as the documentation points out:
"This variable is unused. It is deprecated as of MySQL 5.6.7 and will be removed in a future MySQL release."