1.如果您使用的是MySQL 8.0版，您可以尝试使用JSON_TABLE函数（在dbfiddle上测试）

SELECT DISTINCT tmp.city
FROM table_cities c,
JSON_TABLE(
  c.cities,
  '$[*]'
  COLUMNS(
  city VARCHAR(10) PATH '$[0]'
  )
) tmp;

1.对于MariaDB 10.4.2，您可以尝试此操作。（在dbfiddle上测试）

CREATE TABLE main_table (
    cities VARCHAR(1000)
);

-- create procedure
CREATE PROCEDURE proc1()
BEGIN
SET @index := 0;
SELECT @json_length := MAX(JSON_LENGTH(cities))
FROM table_cities;

REPEAT
   INSERT INTO main_table (cities)
   SELECT JSON_EXTRACT(cities,CONCAT("$[",@index,"]")) FROM table_cities;
   SET @index = @index + 1;
UNTIL @index = @json_length 
END REPEAT;
END;

-- call procedure
CALL proc1;

-- query result
SELECT DISTINCT REPLACE(cities, '"', '') AS city 
FROM main_table
WHERE cities IS NOT NULL;