# File activerecord/lib/arel.rb, line 37
def self.sql(raw_sql)
  Arel::Nodes::SqlLiteral.new raw_sql
end

Wrap a known-safe SQL string for passing to query methods, e.g.

Post.order(Arel.sql("length(title)")).last

Great caution should be taken to avoid SQL injection vulnerabilities. This method should not be used with unsafe values such as request parameters or model attributes.