Hierarchical Data - Nested Dial Model: MySql

Question

I am just learning how to implement a nested set model, but still confuse it with a certain aspect related to elements that can be part of several categories. Given the example below, which was ripped out HERE and reflects many other examples that I came across ...

How to avoid duplication in the database when adding apples, since they are colorful (i.e. red, yellow, green)?

Answer 1

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Answer 2

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Answer 3

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Answer 4

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