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module Sequel module EmulateOffsetWithRowNumber # Emulate OFFSET support with the ROW_NUMBER window function # # The implementation is ugly, cloning the current dataset and modifying # the clone to add a ROW_NUMBER window function (and some other things), # then using the modified clone in a subselect which is selected from. # # If offset is used, an order must be provided, because the use of ROW_NUMBER # requires an order. def select_sql return super unless o = @opts[:offset] order = @opts[:order] || default_offset_order if order.nil? || order.empty? raise(Error, "#{db.database_type} requires an order be provided if using an offset") end columns = clone(:append_sql=>'').columns dsa1 = dataset_alias(1) rn = row_number_column sql = @opts[:append_sql] || '' subselect_sql_append(sql, unlimited. unordered. select_append{ROW_NUMBER(:over, :order=>order){}.as(rn)}. from_self(:alias=>dsa1). select(*columns). limit(@opts[:limit]). where(SQL::Identifier.new(rn) > o). order(rn)) sql end private # The default order to use for datasets with offsets, if no order is defined. # By default, orders by all of the columns in the dataset. def default_offset_order clone(:append_sql=>'').columns end end end
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10 entries across 10 versions & 1 rubygems