It's probably best to say that initially, the question you are trying to ask is meaningless.
In order to understand why, you should research exactly what a "decibel" is and how it is used.
To summarise the key points, 'dB' is not an absolute reference to a measurement of anything, it is a way of describing relative measurements based on a known reference. In order for this to be meaningful, you have to know what your reference point is.
With Decibels and audio, there can be many reference values. When you are using the term "0dB" this basically means that the value is the same as another 'absolute' value.
Start with a measurement that has a known reference, like:
0dBU, or 0dBV or 0dBSPL
a measurement of 0dBU increased by 3dB would equal +3dBU.
A measurement of 0dBU changed by 0dB would equal 0dBU
A measurement of 0dBV changed by -5dB would equal -5dBU
This is a bit more meaningful and hopefully makes more sense.