NOW、CURRENT_TIMESTAMP和SYSDATE:都是傳回系統的目前時間;
mysql> SELECT NOW(),CURRENT_TIMESTAMP(),SYSDATE();
+---------------------+---------------------+---------------------+
| NOW() | CURRENT_TIMESTAMP() | SYSDATE() |
+---------------------+---------------------+---------------------+
| 2014-01-12 15:24:24 | 2014-01-12 15:24:24 | 2014-01-12 15:24:24 |
+---------------------+---------------------+---------------------+
1 row in set (0.06 sec)
這三個函數傳回的都是目前的時間,按上面的例子而言,好像功能是相同的;
mysql> SELECT NOW(),CURRENT_TIMESTAMP(),SYSDATE(),
-> SLEEP(2),
-> NOW(),CURRENT_TIMESTAMP(),SYSDATE();
+---------------------+---------------------+---------------------+----------+--
-------------------+---------------------+---------------------+
| NOW() | CURRENT_TIMESTAMP() | SYSDATE() | SLEEP(2) | N
OW() | CURRENT_TIMESTAMP() | SYSDATE() |
+---------------------+---------------------+---------------------+----------+--
-------------------+---------------------+---------------------+
| 2014-01-12 15:30:52 | 2014-01-12 15:30:52 | 2014-01-12 15:30:52 | 0 | 2
014-01-12 15:30:52 | 2014-01-12 15:30:52 | 2014-01-12 15:30:54 |
+---------------------+---------------------+---------------------+----------+--
-------------------+---------------------+---------------------+
1 row in set (2.00 sec)
加入SLEEP函數,讓其等待2秒,這時發現SYSDATE()和NOW(),CURRENT_TIMESTAMP()傳回的時間是不同的;
原因:
CURRENT_TIMESTAMP是NOW的同義詞,即兩者是相同的;
SYSDATE函數傳回的是執行到目前函數的時間,而NOW傳回的是執行SQL語句時的時間;
對于NOW函數,不管是在SLEEP()函數之前或之後執行,傳回的都是執行這條SQL語句時的時間;