# module ActiveRecord::Querying

### Public Instance Methods

count_by_sql(sql) click to toggle source

Returns the result of an SQL statement that should only include a COUNT(*) in the SELECT part. The use of this method should be restricted to complicated SQL queries that can't be executed using the ActiveRecord::Calculations class methods. Look into those before using this.

    Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"
    # => 12

#### Parameters¶ ↑

- `sql` - An SQL statement which should return a count query from the database, see the example above.

    # File lib/active_record/querying.rb, line 64
    def count_by_sql(sql)
      connection.select_value(sanitize_sql(sql), "#{name} Count").to_i
    end

find_by_sql(sql, binds = [], preparable: nil, &block) click to toggle source

Executes a custom SQL query against your database and returns all the results. The results will be returned as an array with columns requested encapsulated as attributes of the model you call this method from. If you call `Product.find_by_sql` then the results will be returned in a `Product` object with the attributes you specified in the SQL query.

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

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

    # A simple SQL query spanning multiple tables
    Post.find_by_sql "SELECT p.title, c.author FROM posts p, comments c WHERE p.id = c.post_id"
    # => [#<Post:0x36bff9c @attributes={"title"=>"Ruby Meetup", "first_name"=>"Quentin"}>, ...]

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

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

    # File lib/active_record/querying.rb, line 38
    def find_by_sql(sql, binds = [], preparable: nil, &block)
      result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds, preparable: preparable)
      column_types = result_set.column_types.dup
      columns_hash.each_key { |k| column_types.delete k }
      message_bus = ActiveSupport::Notifications.instrumenter

      payload = {
        record_count: result_set.length,
        class_name: name
      }

      message_bus.instrument("instantiation.active_record", payload) do
        result_set.map { |record| instantiate(record, column_types, &block) }
      end
    end