MySQL 8.0

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create table test (user_id int, status varchar(20));
create unique index ui1_test on test
  (user_id, (case when status = 'active' then status end));

Records: 0  Duplicates: 0  Warnings: 0


insert into test (user_id, status) values (1, 'active');
insert into test (user_id, status) values (1, 'active');

Duplicate entry '1-active' for key 'test.ui1_test'


insert into test (user_id, status) values (1, 'inactive');
insert into test (user_id, status) values (1, 'inactive');
insert into test (user_id, status) values (1, 'inactive');
insert into test (user_id, status) values (1, 'processed');
insert into test (user_id, status) values (1, 'processed');
select * From test;


user_id
status


1
active

1
inactive

1
inactive

1
inactive

1
processed

1
processed