What happens if you redeem a code for an app you already bought?

[Kendo]

This applies to movies and music as well. If you already bought an app/movie/song and you are given a redemption code, will iTunes tell you that you already own the app? I've read somewhere that iTunes will redeem the code (even though you already own it), thus wasting away the code.

 

[Sirious]

If you already have it, the code is already wasted at that point.