MySQL 8.0

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select version();


version()


8.0.18


CREATE TABLE country (
    code   int
  , name   int
);

INSERT INTO country VALUES
    (1, 1)
  , (2, 2)
  , (3, 3)
  , (4, 4)
;

CREATE TABLE city (
    countrycode   int
  , population    int
);

INSERT INTO city VALUES
    (1,  50)
  , (1, 200)
  , (3, 300)
  , (4,  10)
  , (4,  20)
;
 select code c, name
   From country
  where 100 > ANY (select population
                     from city
                    where countrycode = country.code
              )
;


c
name


1
1

4
4


 select code c, name
   From country
  where 100 > ALL (select population
                     from city
                    where countrycode = country.code
              )
;


c
name


2
2

4
4


 select code c, name
   From country
  where 100 >     (select population
                     from city
                    where countrycode = country.code
              )
;
show errors;


Level
Code
Message


Error
1242
Subquery returns more than 1 row


 select code c, name
   From country
  where 100 IN    (select population
                     from city
                    where countrycode = country.code
              )
;