You mean 7z the raw SQL? Just as a preemptive check before moving to Clickhouse?
7z the csv. Get a million rows from your table. Compare the csv to the 7z. That will give you a good idea on what kind of compression you will see.
I have very redundant data. I often see 10:1 compression. It's a lot less when I have hashes, addresses and timestamps.
In addition, columnar format like the one used by Click House can often be compressed even better than row format like CSV due to the similarity between value in a column.
And no need to play with columns ordering like with psql: