SQL query to get repeating column value that have other columns in a certain codition - sql

Question

Let's say we have below table of below schema.
create table result
(
id int,
task_id int,
test_name string,
test_result string
);
And dataset populated on this table looks like this.
insert into result
values (1, 1, 'test_a', 'pass'),
(2, 1, 'test_b', 'fail'),
(3, 1, 'test_c', 'pass'),
(4, 1, 'test_d', 'pass'),
(5, 2, 'test_a', 'pass'),
(6, 2, 'test_b', 'pass'),
(7, 2, 'test_c', 'pass'),
(8, 2, 'test_d', 'pass');
Basically single task has multiple test results entry. I want to retrieve task_id that has test_b fail but all the other test passed. So in this example it should return only task_id: 1.
I've tried with EXISTS and HAVING but it doesn't seem working in this case. I'm new to SQL. How can I implement it?

Answer 1

I would just use aggregation with a having clause:
select task_id
from result
group by task_id
having sum(case when test_name = 'test_b' and test_result = 'fail' then 1 else 0 end) = 1 and
sum(case when test_result = 'pass' then 1 else 0 end) = count(*) - 1;
The first condition validates that test_b failed. The second counts the number of passes and it should be one less then the number of rows for the task.
If your database supports except (or minus), you an use set-based operations:
select task_id
from result
where test_name = 'test_b' and test_result = 'fail'
except
select task_id
from result
where test_name <> 'test_b' and test_result = 'fail'

Answer 2

Maybe selecting distinct task IDs that have a fail result:
select distinct [task_id], [task_result]
from [result]
where [task_result] = 'fail'
Note that this query will scan the entire table unless there is an index on task_result.

Answer 3

Following code first sums test takers per task and counts fro 'test_b' whether it failed or not. Outer select ensure 'test_b' failed and other have passed.
select task_id from (
select
task_id,
count(test_result) numberoftakers,
sum(case when test_result<>'pass' AND test_name='test_b' then 1 else 0 end) numberoffailb,
sum(case when test_result='pass' then 1 else 0 end) numberofallpasses
from result
group by task_id) a
where numberoftakers=numberoffailb+numberofallpasses and numberoffailb=1

Answer 4

Assuming that (task_id, task_name) is a unique key of your table, you can indeed use (not) exists, along with a correlated subqueries wich ensures that other records having the same task_id did not passed.
select task_id
from result r
where
test_name = 'test_b'
and test_result = 'fail'
and not exists (
select 1
from result r1
where
r1.task_id = r.task_id
and r1.id != r.id
and r1.test_result = 'fail'
)
The left join antipattern also comes to mind:
select r.task_id
from result r
left join result r1
on r1.task_id = r.task_id
and r1.id != r.id
and r1.test_result = 'fail'
where
r.test_name = 'test_b'
and r.test_result = 'fail'
and r1.id is null
Demo on DB Fiddle - Both queries return:
| task_id |
| :------ |
| 1 |