Functions are special mappings, and mappings are not necessarily functions. Such as: a uniquely corresponds to y; A and b correspond to y; A, b, c and y can all be regarded as mappings, one-to-one and many-to-one.

But it is not one-to-many, for example: y 2 = ax (a is a constant), which is a function, but it is not a mapping, because one x can correspond to two y's here.