Syntax:
SLEEP(duration)

Sleeps (pauses) for the number of seconds given by the duration
argument, then returns 0. If SLEEP() is interrupted, it returns 1. The
duration may have a fractional part. If the argument is NULL or
negative, SLEEP() produces a warning, or an error in strict SQL mode.

URL: http://dev.mysql.com/doc/refman/5.7/en/miscellaneous-functions.html

