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Contents
module Bmg
module Sql
class Processor
class SemiJoin < Processor
include JoinSupport
def initialize(right, on, negate = false, builder)
super(builder)
@right = right
@on = on
@negate = negate
end
attr_reader :right, :on, :negate
def call(sexpr)
if sexpr.set_operator?
call(builder.from_self(sexpr))
elsif right.set_operator?
SemiJoin.new(builder.from_self(right), negate, builder).call(sexpr)
else
super(sexpr)
end
end
private
def apply_join_strategy(left, right)
predicate = build_semijoin_predicate(left, right)
expand_where_clause(left, negate ? !predicate : predicate)
end
def build_semijoin_predicate(left, right)
if right.is_table_dee?
right.where_clause.predicate
else
commons = self.on
subquery = Clip.new(commons, false, :star, builder).call(right)
subquery = Requalify.new(builder).call(subquery)
subquery = All.new(builder).call(subquery)
if commons.size == 0
builder.exists(subquery)
else
join_pre = join_predicate(left, subquery, commons)
subquery = expand_where_clause(subquery, join_pre)
subquery = Star.new(builder).call(subquery)
builder.exists(subquery)
end
end
end
def expand_where_clause(sexpr, predicate)
Grammar.sexpr \
[ :select_exp,
sexpr.set_quantifier,
sexpr.select_list,
sexpr.from_clause,
[ :where_clause, (sexpr.predicate || tautology) & predicate ],
sexpr.order_by_clause,
sexpr.limit_clause,
sexpr.offset_clause ].compact
end
end # class SemiJoin
end # class Processor
end # module Sql
end # module Bmg
Version data entries
18 entries across 18 versions & 1 rubygems