Querying Counts on Field Values in a Single Table - sql

Question

I have a single product table with multiple fields which contain user evaluations of various attributes:
product | attr_1_eval | attr_2_eval | attr_3_eval
ABC | Correct | Incorrect | Null
DEF | Incorrect | Null | Null
XYZ | Undetermined | Null | Incorrect
123 | Null | Undetermined | Correct
456 | Incorrect | Correct | Correct
I need to write a query which totals up those attribute evaluations across all products (where not null):
evaluation | correct | incorrect | undetermined
attr_1 | 1 | 2 | 1
attr_2 | 1 | 1 | 1
attr_3 | 2 | 1 | 0
This SQL gets me part way there:
SELECT
SUM(CASE WHEN attr_1_eval = 'Correct' then 1 else 0 END) AS correct,
SUM(CASE WHEN attr_1_eval = 'Incorrect' then 1 else 0 END) AS incorrect,
SUM(CASE WHEN attr_1_eval = 'Undetermined' then 1 else 0 END) AS undetermined,
SUM(CASE WHEN attr_2_eval = 'Correct' then 1 else 0 END) AS correct,
...
FROM product
But it doesn't group attr_1, attr_2.. by rows with error counts in the columns (as in the desired result set above). I'm using Postgres but help in any flavor of SQL would be most welcome.

Answer 1

Could you do 3 unions?
SELECT
'attr_1' AS evaluation,
SUM(CASE WHEN attr_1_eval = 'Correct' then 1 else 0 END) AS correct,
SUM(CASE WHEN attr_1_eval = 'Incorrect' then 1 else 0 END) AS incorrect,
SUM(CASE WHEN attr_1_eval = 'Undetermined' then 1 else 0 END) AS undetermined
FROM product
UNION
SELECT
'attr_2' AS evaluation,
SUM(CASE WHEN attr_2_eval = 'Correct' then 1 else 0 END) AS correct,
SUM(CASE WHEN attr_2_eval = 'Incorrect' then 1 else 0 END) AS incorrect,
SUM(CASE WHEN attr_2_eval = 'Undetermined' then 1 else 0 END) AS undetermined
FROM product
UNION
SELECT
'attr_3' AS evaluation,
SUM(CASE WHEN attr_3_eval = 'Correct' then 1 else 0 END) AS correct,
SUM(CASE WHEN attr_3_eval = 'Incorrect' then 1 else 0 END) AS incorrect,
SUM(CASE WHEN attr_3_eval = 'Undetermined' then 1 else 0 END) AS undetermined
FROM product
It's not the most elegant/efficient solution probably but it should get what you want

Answer 2

It's a little brute force, and I hate the fact that it scans the table three times, but this does appear to get the desired output. I'm sorry I don't know PostGres, but this should work in Oracle:
select
Attribute_name,
Sum (correct) as Correct,
sum (incorrect) as Incorrect,
sum (undetermined) as Undetermined
from
(
select
'attr_1' as Attribute_Name,
decode (attr_1_eval, 'Correct', 1, 0) as correct,
decode (attr_1_eval, 'Incorrect', 1, 0) as incorrect,
decode (attr_1_eval, 'Undetermined', 1, 0) as undetermined
from product
union all
select
'attr_2',
decode (attr_2_eval, 'Correct', 1, 0),
decode (attr_2_eval, 'Incorrect', 1, 0),
decode (attr_2_eval, 'Undetermined', 1, 0)
from product
union all
select
'attr_3',
decode (attr_3_eval, 'Correct', 1, 0),
decode (attr_3_eval, 'Incorrect', 1, 0),
decode (attr_3_eval, 'Undetermined', 1, 0)
from product
)
group by Attribute_Name