Difference between NOW(), SYSDATE() & CURRENT_DATE() in MySQL - mysql

Question

What difference between NOW() , SYSDATE() , CURRENT_DATE() in MySQL and where it can be used in real scenario .
I tried NOW(),SYSDATE(),Current_Date() when I insert data into a table and column datatype is TIMESTAMP all are given same date and time.

Answer 1

Current_date() will only give you the date.
now() give you the datetime when the statement,procedure etc... started.
sysdate() give you the current datetime.
Look at the seconds after waiting 5 seconds between now()1 sysdate()1 with the following query (scroll to the right):
select now(),sysdate(),current_date(),sleep(5),now(),sysdate();
-- will give
-- now() sysdate() current_date() sleep(5) now()1 sysdate()1
-- 6/10/2014 2:50:04 AM 6/10/2014 2:50:04 AM 6/10/2014 12:00:00 AM 0 6/10/2014 2:50:04 AM 6/10/2014 2:50:09 AM

Answer 2

NOW() returns a constant time that indicates the time at which the statement began to execute. (Within a stored function or trigger, NOW() returns the time at which the function or triggering statement began to execute.) This differs from the behavior for SYSDATE(), which returns the exact time at which it executes.
mysql> SELECT NOW(), SLEEP(2), NOW();
+---------------------+----------+---------------------+
| NOW() | SLEEP(2) | NOW() |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:36 | 0 | 2006-04-12 13:47:36 |
+---------------------+----------+---------------------+
mysql> SELECT SYSDATE(), SLEEP(2), SYSDATE();
+---------------------+----------+---------------------+
| SYSDATE() | SLEEP(2) | SYSDATE() |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:44 | 0 | 2006-04-12 13:47:46 |
+---------------------+----------+---------------------+

Answer 3

Current_date returns the time stamp of the client while sysdate returns the time stamp of the server. If both server and the client are on the same machine, then, the result of both commands are the same. But in case that your sever is for example in USA and your clients are in China, then, these two functions return completely different results.
I don't know about thew now(), sorry :-)

Answer 4

One of the major differences between sysdate() and now() recently bit me in the behind. It was the difference in the point-in-time and frequency of their execution. sysdate() is evaluated every time within the same statement--ie, in every row to which it applies. But now() will only be evaluated only once, which is at the start of query execution.
This difference isn't noticeable when there are only a few rows. But it's very significant when there are millions of rows. In RHEL7, for example, sysdate() apparently makes a costly system call, so that when there are millions of rows, using sysdate() took more than an hour, but using now() in the exact same statement took only several seconds!
This is on top of precision issues, because sysdate() will return a different value, for example, between time t and time t+50 millis.
With regard to curdate(), I was also wondering how it's different from either now() or sysdate(). The MySQL Reference says that, with regard to when and how many times it's executed, curdate() behaves like now().
Reference: MySQL 5.7 Reference - Date and Time Functions -- All of the above is described in this page. However, it's scattered on the page, so you'll have to read through the overview section as well as the reference for each function.

Answer 5

CURRENT_DATE() is a synonym for many other similar functions all of which provide only the date.
There is a subtle difference between NOW() and SYSDATE() which you can read up more on this official MySQL website page.

Answer 6

CURRENT_DATE is static and works better with date indexes.
NOW() seems dynamic and does not benefit from index. (I would love to hear a comment on the subject with more detail on the MySQL internals here!)
Here's a real-world example using NOW():
explain SELECT DISTINCT e.manager_id, m.manager_name FROM events e JOIN manager m ON m.manager_id = e.manager_id
WHERE m.manager_name != '' AND e.event_when > NOW() - INTERVAL 1 YEAR;
+---------+----------+------------------------------+
| rows | filtered | Extra |
+---------+----------+------------------------------+
| 1333648 | 29.06 | Using where; Using temporary |
| 1 | 90.59 | Using where |
+---------+----------+------------------------------+
You can see the number of rows are reduced substantially using CURRENT_DATE (or CURRENT_TIMESTAMP):
explain SELECT DISTINCT e.manager_id, m.manager_name FROM events e JOIN manager m ON m.manager_id = e.manager_id
WHERE m.manager_name != '' AND e.event_when > CURRENT_DATE - INTERVAL 1 YEAR;
+--------+----------+----------------------------------------+
| rows | filtered | Extra |
+--------+----------+----------------------------------------+
| 361470 | 100.00 | Using index condition; Using temporary |
| 1 | 90.59 | Using where |
+--------+----------+----------------------------------------+

Answer 7

NOW() returns a constant time that indicate's the time at which the statement began to exicute whereas SYSDATE () returns the time at which it exicute... OR in other words NOW ()shows query exicution time and SYSDATE() shows self exicution time..