presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitSelectSingle
class AstBuilder:    @Override
    public Node visitSelectSingle(SqlBaseParser.SelectSingleContext context)
    {
        return new SingleColumn(
                getLocation(context),
                (Expression) visit(context.expression()),
                visitIfPresent(context.identifier(), Identifier.class));
    }