How to execute raw SQL in Rails

Execute raw SQL directly from ActiveRecord::Base or ApplicationRecord inherited from ActiveRecord::Base

sql = 'SELECT * from tables;'

results = ActiveRecord::Base.connection.execute(sql)
results = ApplicationRecord.connection.execute(sql)

# results will contain PG::Result object, eg:
#<PG::Result:0x00007f9eb76637c8 status=PGRES_TUPLES_OK ntuples=1 nfields=7 cmd_tuples=1>

Access results

results.each do |r|
  puts r
end

Reference

How do you manually execute SQL commands in Ruby On Rails using NuoDB
Executing raw sql against multiple data bases
Understanding PG Result object