Module | Sequel::EmulateOffsetWithRowNumber |
In: |
lib/sequel/adapters/utils/emulate_offset_with_row_number.rb
|
If the offset must be emulated with ROW_NUMBER, don‘t remove any ordering, because it can cause invalid queries to be issued if an offset is required when ordering.
# File lib/sequel/adapters/utils/emulate_offset_with_row_number.rb, line 8 8: def empty? 9: return super unless emulate_offset_with_row_number? 10: get(Sequel::SQL::AliasedExpression.new(1, :one)).nil? 11: end
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.
# File lib/sequel/adapters/utils/emulate_offset_with_row_number.rb, line 21 21: def select_sql 22: return super unless emulate_offset_with_row_number? 23: 24: offset = @opts[:offset] 25: order = @opts[:order] 26: if require_offset_order? 27: order ||= default_offset_order 28: if order.nil? || order.empty? 29: raise(Error, "#{db.database_type} requires an order be provided if using an offset") 30: end 31: end 32: 33: columns = clone(:append_sql=>String.new, :placeholder_literal_null=>true).columns 34: dsa1 = dataset_alias(1) 35: rn = row_number_column 36: sql = @opts[:append_sql] || String.new 37: subselect_sql_append(sql, unlimited. 38: unordered. 39: select_append{ROW_NUMBER{}.over(:order=>order).as(rn)}. 40: from_self(:alias=>dsa1). 41: select(*columns). 42: limit(@opts[:limit]). 43: where(SQL::Identifier.new(rn) > offset). 44: order(rn)) 45: sql 46: end