MariaDB 10.3

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CREATE TABLE tablename (
  `Name` VARCHAR(1),
  `Code` INTEGER
);

INSERT INTO tablename
  (`Name`, `Code`)
VALUES
  ('A', '200'),
  ('B', '300'),
  ('C', '300'),
  ('D', '400'),
  ('E', '400'),
  ('F', '400'),
  ('G', '400');
with cte as (
  select *,
    row_number() over (partition by code order by name) rn,
    count(*) over (partition by code) counter
  from tablename  
)
select Name, Code
from cte
where rn <= ceiling(counter * 0.50)


Name
Code


A
200

B
300

D
400

E
400


with cte as (
  select *,
    row_number() over (partition by code order by name) rn,
    count(*) over (partition by code) counter
  from tablename  
)
select Name, Code
from cte
where rn <= counter * 0.50 or rn = 1


Name
Code


A
200

B
300

D
400

E
400