Question

When I run a sleep command in MySQL, e.g. SELECT SLEEP(7), it returns zero. Why is this? Is it following the standard Unix convention of return values? Does it just need something to return and so zero is a good harmless value? Are there other MySQL functions that behave like this?

Answer 1

From the documentation:

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 given in microseconds. This
function was added in MySQL 5.0.12.