MySQL 5.6

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CREATE TABLE `executed_tests` (
    `id` INTEGER AUTO_INCREMENT NOT NULL,
    `user_id` INTEGER NOT NULL,
    `test_id` INTEGER NOT NULL,
    `start_date` DATE NOT NULL,
    `completed_date` DATE,
    `is_open` BOOLEAN,
    PRIMARY KEY (`id`),
    UNIQUE(`user_id`, `test_id`, `is_open`)
);
insert into executed_tests (user_id, test_id, start_date, is_open) values (1, 2, '1981-08-24', true);
select * from executed_tests;


id
user_id
test_id
start_date
completed_date
is_open


1
1
2
1981-08-24
null
1


insert into executed_tests (user_id, test_id, start_date, is_open) values (1, 2, '1981-08-24', true);
Duplicate entry '1-2-1' for key 'user_id'

select * from executed_tests;


id
user_id
test_id
start_date
completed_date
is_open


1
1
2
1981-08-24
null
1


insert into executed_tests (user_id, test_id, start_date, completed_date) values (1, 2, '1981-08-24', '1981-08-24');
select * from executed_tests;


id
user_id
test_id
start_date
completed_date
is_open


1
1
2
1981-08-24
null
1

3
1
2
1981-08-24
1981-08-24
null


insert into executed_tests (user_id, test_id, start_date, completed_date) values (1, 2, '1981-08-24', '1981-08-24');
select * from executed_tests;


id
user_id
test_id
start_date
completed_date
is_open


1
1
2
1981-08-24
null
1

3
1
2
1981-08-24
1981-08-24
null

4
1
2
1981-08-24
1981-08-24
null

id	user_id	test_id	start_date	completed_date	is_open
1	1	2	1981-08-24	null	1
3	1	2	1981-08-24	1981-08-24	null
4	1	2	1981-08-24	1981-08-24	null