presto-main/src/main/java/io/prestosql/sql/analyzer/AggregationAnalyzer.java/AggregationAnalyzer/visitExists
class AggregationAnalyzer:        @Override
        protected Boolean visitExists(ExistsPredicate node, Void context)
        {
            checkState(node.getSubquery() instanceof SubqueryExpression);
            return process(node.getSubquery(), context);
        }