When an NFT Collection appears on Ethereum we have two different identifiers, a contract address for the NFT Collection, and an ID number for every NFT in the collection if we use both columns in the Ethereum.core.ez_nft_sales from Flipside we can have exactly the number of Unique NFTs being sold with:

Count(Distinct NFT_ADDRESS, TOKENID) 

With that, we have the number of Unique NFTs (ID) from all the NFTs Collections.

To get the amount of NFT Sales I'll use:

Count(*)

A single transaction hash could have more than 1 NFT Sale, and thats the reason to use * instead of tx_hash, as every row from this table is an NFT Sale.

There are sometimes NFT Projects that release multiples NFT Collections and that's the reason we have a column called PROJECT_NAME, and this column will add multiples NFT Collections related to the same NFT Projects, using this column is wrong to compare NFT Collections by themselves as some projects could have more than 5 or more NFT collections leading to wrong results because the data will be about NFT Projects and not unique NFT Collections.

NFT Activity on Ethereum