presto-main/src/main/java/io/prestosql/sql/analyzer/ExpressionAnalyzer.java/ExpressionAnalyzer/visitExists
class ExpressionAnalyzer:        @Override
        protected Type visitExists(ExistsPredicate node, StackableAstVisitorContext<Context> context)
        {
            StatementAnalyzer analyzer = statementAnalyzerFactory.apply(node);
            Scope subqueryScope = Scope.builder().withParent(context.getContext().getScope()).build();
            analyzer.analyze(node.getSubquery(), subqueryScope);

            existsSubqueries.add(NodeRef.of(node));

            return setExpressionType(node, BOOLEAN);
        }