MySQL 5.7

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create table customer (id int auto_increment primary key,
grade int, city varchar(12))
insert into customer (grade, city) values
(4, 'Columbo'),
(8, 'Los Angeles')
    SELECT *
    FROM customer
    WHERE grade > 
       (SELECT MAX(grade)
        FROM customer
        WHERE city='New York');
SELECT *
FROM customer
WHERE grade > 
   (SELECT COALESCE(MAX(grade), -1)
    FROM customer
    WHERE city='New York');


id
grade
city


1
4
Columbo

2
8
Los Angeles


insert into customer (grade, city) values
(5, 'New York')
SELECT *
FROM customer
WHERE grade > 
   (SELECT COALESCE(MAX(grade), -1)
    FROM customer
    WHERE city='New York');


id
grade
city


2
8
Los Angeles