Description

iszero returns one if its argument is an integer 0, a float 0.0 or a double 0.0 For any other arguments, of whatever type, it will return zero.

iszero(0)               -> 1 (Yes it is)
iszero(0.0)             -> 1 (Double precision zero also
                                is a zero)
iszero(atof('0.0'))     -> 1 (As well as single
                                precision floating point)
iszero(1)               -> 0 (No, it's not)
iszero('Cifra')         -> 0 (neither is this one)
iszero(NULL)            -> 0 (nor this one)