Question: I have stored procedure which returns around 100 rows. One column is Category. 

In SSRS, I've created DataSet related to that stored procedure. On Report body I have Tablix, which I relate to DataSet.

Now, I have additional parameter, called FilterColumn, which consist all different categories from dataset, plus one row called "All products". 

How to filter tablix based on that parameter to show me whether products from specific categories or all products?

Answer: 
You need to set up a filter similar to the following:

![enter image description here](https://i.stack.imgur.com/T2230.png)

Where the expression is:

```
=IIf(Parameters!FilterColumn.Value = Fields!Category.Value
        or Parameters!FilterColumn.Value = "All products"
    , "Include"
    , "Exclude")

```

This matches the row *Category* based on the parameter value, or, if the value = `All products`, will include all rows.

As mentioned in the comments and the other answer, this is possible in the SP too, but since it seems to be specifically to demonstrate the functionality this should do the trick at the report level.
Pass the Additional Parameter to your store procedure, so you send data that is already sorted to your report. This will avoid multiple Tablix created depending on your parameter selection.