test.rb

SHARD_REGEXP = %r{("?)(canvas|cluster\d+(?:_shard_\d+)?)\1\.}.freeze
query = 'select * from "cluster123_shard_3".xx join cluster123_shard_3.yy on a = b'

counts = Hash.new(0)
n_query = query.gsub(SHARD_REGEXP) do | s | counts[s]+=1; "SOME_SHARD."; end

# At the end counts is:
# {"\"cluster123_shard_3\"."=>1, "cluster123_shard_3."=>1}
# And I'd like it to be:
# {"cluster123_shard_3"=>2}