module ActiveRecord::Querying

def count_by_sql(sql)

Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"

* +sql+ - An SQL statement which should return a count query from the database, see the example below.

==== Parameters

using the ActiveRecord::Calculations class methods. Look into those before using this.
The use of this method should be restricted to complicated SQL queries that can't be executed
Returns the result of an SQL statement that should only include a COUNT(*) in the SELECT part. 
def count_by_sql(sql)
  sql = sanitize_conditions(sql)
  connection.select_value(sql, "#{name} Count").to_i
end

def find_by_sql(sql, binds = [])

Post.find_by_sql ["SELECT body FROM comments WHERE author = :user_id OR approved_by = :user_id", { :user_id => user_id }]
Post.find_by_sql ["SELECT title FROM posts WHERE author = ? AND created > ?", author_id, start_date]

You can use the same string replacement techniques as you can with ActiveRecord::QueryMethods#where:

# => [#"Ruby Meetup", "first_name"=>"Quentin"}>, ...]
Post.find_by_sql "SELECT p.title, c.author FROM posts p, comments c WHERE p.id = c.post_id"
# A simple SQL query spanning multiple tables

change your call if you switch engines.
MySQL specific terms will lock you to using that particular database engine or require you to
no database agnostic conversions performed. This should be a last resort because using, for example,
The +sql+ parameter is a full SQL query as a string. It will be called as is, there will be

table.
SELECT will be attributes of the model, whether or not they are columns of the corresponding
If you call a complicated SQL query which spans multiple tables the columns specified by the

a +Product+ object with the attributes you specified in the SQL query.
this method from. If you call Product.find_by_sql then the results will be returned in
be returned as an array with columns requested encapsulated as attributes of the model you call
Executes a custom SQL query against your database and returns all the results. The results will 
def find_by_sql(sql, binds = [])
  result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds)
  column_types = {}
  if result_set.respond_to? :column_types
    column_types = result_set.column_types
  else
    ActiveSupport::Deprecation.warn "the object returned from `select_all` must respond to `column_types`"
  end
  result_set.map { |record| instantiate(record, column_types) }
end