How to obtain the start time of an execution unit using the NOW() function?

NOW(prec) is a MySQL built-in function that returns the start time of an execution unit with a given precision of fractional seconds. For example:

SELECT NOW(), SLEEP(2), NOW();
  -- +---------------------+----------+---------------------+
  -- | NOW()               | SLEEP(2) | NOW()               |
  -- +---------------------+----------+---------------------+
  -- | 2023-11-22 11:43:07 |        0 | 2023-11-22 11:43:07 |
  -- +---------------------+----------+---------------------+

SELECT NOW(), NOW()+1;
  -- +---------------------+----------------+
  -- | NOW()               | NOW()+1        |
  -- +---------------------+----------------+
  -- | 2023-11-22 12:02:40 | 20231122120241 |
  -- +---------------------+----------------+

SELECT NOW(6), NOW(6)+1;
  -- +----------------------------+-----------------------+
  -- | NOW(6)                     | NOW(6)+1              |
  -- +----------------------------+-----------------------+
  -- | 2023-11-22 12:03:08.505415 | 20231122120309.505415 |
  -- +----------------------------+-----------------------+

Note that NOW() returns the start time of an execution unit like a statement, a stored function or a trigger. Calling NOW() multiple times will give you the same timestamp.

SELECT NOW(), SLEEP(2), NOW();
  -- +---------------------+----------+---------------------+
  -- | NOW()               | SLEEP(2) | NOW()               |
  -- +---------------------+----------+---------------------+
  -- | 2023-11-22 12:05:07 |        0 | 2023-11-22 12:05:07 |
  -- +---------------------+----------+---------------------+

Reference information of the NOW() function:

NOW(prec): tm
  Returns a constant time that indicates the time at which the statement,
  a stored function or a trigger, began to execute.

  Returns the current timestamp as a value in 'YYYY-MM-DD hh:mm:ss.SSSSSS' or
  YYYYMMDDhhmmss.SSSSSS format, depending on whether the function is
  used in string or numeric context.

Arguments, return value and availability:
  prec: Optional. Default is 0. The precision of fractional seconds.
  tm: Return value. The start time of the execution unit.
  Available since MySQL 4.

Related MySQL functions:

• LOCALTIME() - Synonym for NOW()
• LOCALTIMESTAMP() - Synonym for NOW()
• SYSDATE() - Current Timestamp

⇒ PERIOD_ADD() - Adding Months to Period

⇐ MONTHNAME() - Name of Month

⇑ MySQL Functions on Date and Time

⇑⇑ MySQL Function References