MySQL 8.0

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create table test
(
    id    varchar(255) not null
        primary key,
    price varchar(10)  not null,
    link  varchar(255) not null
);

insert into test values
(1,	'50',	'text'),
(2,	'50',	'text'),
(3, '50 USD',	'text');

Records: 3  Duplicates: 0  Warnings: 0


update test set link = 'a' where REGEXP_SUBSTR(price,"[0-9]+") <= 50;

Rows matched: 3  Changed: 3  Warnings: 0


select *, CAST(price AS UNSIGNED)
from test


id
price
link
CAST(price AS UNSIGNED)


1
50
a
50

2
50
a
50

3
50 USD
a
50