MySQL 8.0

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create table mytable (id int, js json);
insert into mytable values(1, '["The Cherries:2.50","Draw:3.25","Swansea Jacks:2.87"]');
select * from mytable


id
js


1
5b225468652043686572726965733a322e3530222c2022447261773a332e3235222c20225377616e736561204a61636b733a322e3837225d


select 
    t.id, 
    json_arrayagg(json_object(
        'name', substring(j.val, 1, locate(':', j.val) - 1), 
        'odds', substring(j.val, locate(':', j.val) + 1)
    )) new_js
from mytable t
cross join json_table(t.js, '$[*]' columns (val varchar(500) path '$')) as j
group by t.id


id
new_js


1
[{"name": "The Cherries", "odds": "2.50"}, {"name": "Draw", "odds": "3.25"}, {"name": "Swansea Jacks", "odds": "2.87"}]