def exact_aggregates(self, query):
child_scope = Scope()
if self.options.row_privacy:
keycount_expr = AggFunction("COUNT", None, AllColumns())
else:
key_col = self.key_col(query)
keycount_expr = AggFunction("COUNT", "DISTINCT", Column(key_col))
child_scope.push_name(keycount_expr.expression)
for ne in query.select.namedExpressions:
child_scope.push_name(ne.expression)
keycount = NamedExpression("keycount", keycount_expr)
select = Seq([keycount] + [ne for ne in query.select.namedExpressions])
select = Select(None, select)
subquery = Query(child_scope.select(), query.source, query.where, query.agg, None, None, None)
if self.options.reservoir_sample and not self.options.row_privacy:
subquery = self.per_key_random(subquery)
subquery = [AliasedRelation(subquery, "per_key_random")]
filtered = Where(BooleanCompare(Column("per_key_random.row_num"), "<=", Literal(str(self.options.max_contrib), self.options.max_contrib)))
return Query(select, From(subquery), filtered, query.agg, None, None, None)
else:
subquery = self.per_key_clamped(subquery)
subquery = [AliasedRelation(subquery, "per_key_all")]
return Query(select, From(subquery), None, query.agg, None, None, None)
def query(self, query):
query = QueryParser(self.metadata).query(str(query))
Validate().validateQuery(query, self.metadata)
child_scope = Scope()
# we make sure aggregates are in select scope for subqueries
if query.agg is not None:
for ge in query.agg.groupingExpressions:
child_scope.push_name(ge.expression)
select = Seq([
self.rewrite_outer_named_expression(ne, child_scope)
for ne in query.select.namedExpressions
])
select = Select(None, select)
subquery = Query(child_scope.select(), query.source, query.where,
query.agg, query.having, None, None)
subquery = self.exact_aggregates(subquery)
subquery = [AliasedRelation(subquery, "exact_aggregates")]
q = Query(select, From(subquery), None, query.agg, None, query.order,
query.limit)
return QueryParser(self.metadata).query(str(q))
def per_key_random(self, query):
key_col = self.key_col(query)
select = Seq([NamedExpression(None, AllColumns()), NamedExpression("row_num", Expression("ROW_NUMBER() OVER (PARTITION BY {0} ORDER BY random())".format(key_col)))])
select = Select(None, select)
subquery = self.per_key_clamped(query)
subquery = [AliasedRelation(subquery, "clamped" if self.options.clamp_columns else "not_clamped")]
return Query(select, From(subquery), None, None, None, None, None)