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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
Version data entries
10 entries across 10 versions & 1 rubygems