mysql - 当运行 UPDATE ... datetime = NOW();所有更新的行都会有相同的日期/时间吗？

Question

当你运行类似的东西时:

UPDATE table SET datetime = NOW();

在具有 1 000 000 000 条记录且查询需要 10 秒才能运行的表上，所有行的时间是否完全相同(分钟和秒)还是不同的时间？换句话说，是查询开始的时间还是每行更新的时间？

我正在运行 MySQL，但我认为这适用于所有数据库。

Answer 1

http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html#function_now

"NOW() returns a constant time that indicates the time at which the statement began to execute. (Within a stored routine or trigger, NOW() returns the time at which the routine or triggering statement began to execute.) This differs from the behavior for SYSDATE(), which returns the exact time at which it executes as of MySQL 5.0.13. "