select parent row where ALL children rows meet criterias - mysql

Question

I have two table, rates and criterias. parent_id in criterias refers to id in rates.
I need to select the rates where ALL children rows in table criterias WHERE criteria_1 AND criteria_2 equal to NULL.
In the example below, only flat rate should be selected
rates
id | name
--------------------
1 | summer rate
2 | flat rate
3 | student rate
conditions
id | parent_id | criteria_1 | criteria_2
------------------------------------------------------
1 | 1 | 523 | 563
2 | 1 | null | null
3 | 2 | null | null
4 | 2 | null | null
5 | 3 | 777 | null
I tried NOT EXIST, but it return it return any rate where one children have two null criteria

Answer 1

try using this subquery with inner join.
select * from
(select * from rates where name = 'flat rate') t1
inner join
(select * from criterias where coalesce(criteria_1, 0) = 0 and coalesce(criteria_2, 0) = 0) t2
on t2.parent_id = t1.id

Answer 2

Please see the following query it should work. You need to compare 2 result set to find rate with ALL null childrens.
SELECT
a.parent_id
FROM(
SELECT
parent_id,
COUNT(*) AS total_count
FROM criterias c
WHERE c. criteria_1 IS NULL AND c.criteria_2 IS NULL
GROUP BY 1
) a
INNER JOIN (
SELECT
parent_id,
COUNT(*) AS total_count
FROM criterias c
GROUP BY 1
)b ON a.parent_id = b.parent_id AND a.total_count = b.total_count

Answer 3

I would use some aggregate function with an having clause grouped by parent_id.
Using a min or max would return a numerical value if there is at least one non-null value per parent_id but will be null if there are only null. So just need to use an having min(<field>) is null to find a parent_id with only null value.
select *
from rates r
where id in(
select parent_id
from criterias
group by parent_id
having min(criteria_1) is null
and min(criteria_2) is null
);
or With an inner join (if you prefer)
select *
from rates r
inner join (
select parent_id
from criterias
group by parent_id
having min(criteria_1) is null
and min(criteria_2) is null
) c ON c.parent_id = r.id;
Validated with :
create table rates(
id int,
name varchar(20)
);
create table criterias (
id int,
parent_id int,
criteria_1 int null,
criteria_2 int null
);
insert into rates values (1, 'summer rate');
insert into rates values (2, 'flate rate');
insert into rates values (3, 'student rate');
insert into rates values (4, 'old rate');
insert into rates values (5, 'any rate');
insert into criterias values (1, 1, 523, 563);
insert into criterias values (2, 1, null, null);
insert into criterias values (3, 2, null, null);
insert into criterias values (4, 2, null, null);
insert into criterias values (5, 1, 777, null);
insert into criterias values (6, 4, null, null);
insert into criterias values (7, 5, null, null);
insert into criterias values (8, 5, null, null);
/*insert into criterias values (9, 5, 1, null);*/
select *
from rates r
where id in(
select parent_id
from criterias
group by parent_id
having min(criteria_1) is null
and min(criteria_2) is null
);
Result:
id name
2 flate rate
4 old rate
5 any rate