MariaDB 10.4

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select version();

version()

10.4.26-MariaDB-1:10.4.26+maria~deb10-log

create table my_table
(id serial primary key
,item varchar(12) not null
,priority int not null
)
insert into my_table values
(1,'item1',20),
(2,'item2',30)

Records: 2  Duplicates: 0  Warnings: 0

select item, SUM(priority) OVER (ORDER BY id) AS cum_prob FROM my_table

item
cum_prob

item1
20

item2
50

SELECT item FROM (select item, SUM(priority) OVER (ORDER BY id) AS cum_prob FROM my_table) as b WHERE cum_prob >= RAND()*100 ORDER BY cum_prob LIMIT 1

item