text: DROP DATABASE IF EXISTS db;
  
  CREATE DATABASE db;
  CREATE TABLE db.t(c1 int) ENGINE = Null;
  SELECT COUNT(1) from system.tables where name = 't' and database = 'db';
  
  CREATE DATABASE IF NOT EXISTS db;
  CREATE DATABASE db; -- {ErrorCode 2301}
  
  DROP DATABASE IF EXISTS db;
  
  CREATE DATABASE system; -- {ErrorCode 2301}
  DROP DATABASE system; -- {ErrorCode 1002}
  