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module Arel
module SqlCompiler
class PostgreSQLCompiler < GenericCompiler
def select_sql
if !relation.orders.blank? && using_distinct_on?
selects = relation.select_clauses
joins = relation.joins(self)
wheres = relation.where_clauses
groups = relation.group_clauses
havings = relation.having_clauses
orders = relation.order_clauses
subquery_clauses = [ "",
"SELECT #{selects.kind_of?(::Array) ? selects.join("") : selects.to_s}",
"FROM #{relation.from_clauses}",
joins,
("WHERE #{wheres.join(' AND ')}" unless wheres.empty?),
("GROUP BY #{groups.join(', ')}" unless groups.empty?),
("HAVING #{havings.join(' AND ')}" unless havings.empty?)
].compact.join ' '
subquery_clauses << " #{locked}" unless locked.blank?
build_query \
"SELECT * FROM (#{build_query subquery_clauses}) AS id_list",
"ORDER BY #{aliased_orders(orders)}",
("LIMIT #{relation.taken}" unless relation.taken.blank? ),
("OFFSET #{relation.skipped}" unless relation.skipped.blank? )
else
super
end
end
def using_distinct_on?
relation.select_clauses.any? { |x| x =~ /DISTINCT ON/ }
end
def aliased_orders(orders)
# 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.
order = orders.join(', ').split(/,/).map { |s| s.strip }.reject(&:blank?)
order = order.zip((0...order.size).to_a).map { |s,i| "id_list.alias_#{i} #{'DESC' if s =~ /\bdesc$/i}" }.join(', ')
end
def supports_insert_with_returning?
engine.connection.send(:postgresql_version) >= 80200
end
end
end
end
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