# We need to handle this in Arel:

# schema_statements.rb

# SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause.
# Both PostgreSQL and Oracle overrides this for custom DISTINCT syntax.
#
#   distinct("posts.id", "posts.created_at desc")
def distinct(columns, order_by)
  "DISTINCT #{columns}"
end

# ORDER BY clause for the passed order option.
# PostgreSQL overrides this due to its stricter standards compliance.
def add_order_by_for_association_limiting!(sql, options)
  sql << " ORDER BY #{options[:order]}"
end

# postsgresql_adapter.rb
# Returns a SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause.
#
# PostgreSQL requires the ORDER BY columns in the select list for distinct queries, and
# requires that the ORDER BY include the distinct column.
#
#   distinct("posts.id", "posts.created_at desc")
def distinct(columns, order_by) #:nodoc:
  return "DISTINCT #{columns}" if order_by.blank?

  # Construct a clean list of column names from the ORDER BY clause, removing
  # any ASC/DESC modifiers
  order_columns = order_by.split(',').collect { |s| s.split.first }
  order_columns.delete_if &:blank?
  order_columns = order_columns.zip((0...order_columns.size).to_a).map { |s,i| "#{s} AS alias_#{i}" }

  # Return a DISTINCT ON() clause that's distinct on the columns we want but includes
  # all the required columns for the ORDER BY to work properly.
  sql = "DISTINCT ON (#{columns}) #{columns}, "
  sql << order_columns * ', '
end

# Returns an ORDER BY clause for the passed order option.
#
# PostgreSQL does not allow arbitrary ordering when using DISTINCT ON, so we work around this
# by wrapping the +sql+ string as a sub-select and ordering in that query.
def add_order_by_for_association_limiting!(sql, options) #:nodoc:
  return sql if options[:order].blank?

  order = options[:order].split(',').collect { |s| s.strip }.reject(&:blank?)
  order.map! { |s| 'DESC' if s =~ /\bdesc$/i }
  order = order.zip((0...order.size).to_a).map { |s,i| "id_list.alias_#{i} #{s}" }.join(', ')

  sql.replace "SELECT * FROM (#{sql}) AS id_list ORDER BY #{order}"
end


# And this:

# database_statements.rb
def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
  "WHERE #{quoted_primary_key} IN (SELECT #{quoted_primary_key} FROM #{quoted_table_name} #{where_sql})"
end

# MysqlAdapter - mysql_adapter.rb
def limited_update_conditions(where_sql, quoted_table_name, quoted_primary_key)
  where_sql
end