How can I create a unique list of data across multiple rows AND columns?

Question

Google Sheets has a UNIQUE() function which when given a column of values, will output a column of all unique values.

This works well for column-specific data, however, you have multiple columns and rows of data that needs to be summarized, this won't work. This is because if you include a 2-dimensional range into UNIQUE() the end results are two dimensional, with only each column being summarized.

Is there a function or way to summarize all values across an entire 2-dimensional range?

REASONING:

I have a large list of businesses. Each column is a type of business, and each row contains values of business names. I need to create an end-list of all businesses that are provided throughout the entire source sheet. I don't need unique values per column. I need unique values across the entire document.

Answer 1

=UNIQUE({A:A;B:B;C:C})

---

=ARRAYFORMULA(UNIQUE(QUERY(TO_TEXT({A:A;B:B;C:C}), 
 "select Col1 where Col1 is not null")))

Answer 2

=unique(flatten(A1:Z))

I think this will work and it worked for me.

Answer 3

I think in your case, you may want to stack the columns vertically. You can do that by adding a semi-colon between them, like this:

=ARRAYFORMULA(UNIQUE(QUERY(TO_TEXT({C:C;D:D;E:E;F:F}), 
 "select Col1 where Col1 is not null")))