I have an Item table:

```
ItemID    ItemNumber    CategoryID
----------------------------------
1         1             1
2         2             1
3         3             1
4         1             2
5         2             2
6         3             2
7         1             3
8         2             3
9         3             3

```

A Category table:

```
CategoryID    CategoryNumber    GenreID
---------------------------------------
1             1                 1
2             2                 2
3             3                 3

```

And a Genre table which is not relevant.

The requirement is for me to make sure that ItemNumber 1 is unique to GenreID 1. i.e., there can be only one Item with an ItemNumber of 1 that is in a category belonging to the Genre with a GenreID of 1.

How do I write a SQL query to get a count of Items with the same ItemNumber in the same Genre, or Items that violate this business rule? It's really boggling my mind and I need expert SQL help.