Enter data for missing category in snowflake - sql

Question

I have a table like
For each keyword, there are 2 devices - mobile and desktop. If entry for only one device is found, then it should automatically create the entry for other device keeping the data in rest of the columns same. I am currently doing a full outer join which is working fine for the case where one device category is missing but generating duplicates where both devices are present. For example,
my current query is giving the result as
select a.keyword, b.device, a.rating
from kw a full outer join kw b
on a.keyword=b.keyword and a.rating=b.rating
How do I get the result as

Answer 1

The first step will be to identify records that don't have a paired record. There's a couple of ways to do this, but the easiest is probably just a quick GROUP BY/HAVING:
SELECT keyword
FROM kw
GROUP BY keyword
HAVING COUNT(*) = 1
You can those join those results back into the original table to generate the new records that are needed:
SELECT sk.keyword,
CASE WHEN kw.device = 'mobile' THEN 'desktop' ELSE 'mobile' END as device,
kw.rating
FROM
(
SELECT keyword
FROM kw
GROUP BY keyword
HAVING COUNT(*) = 1
)sk
INNER JOIN kw ON kw.keyword = sk.keyword
Then you can UNION back in the original table to bring your new records and existing records into a single result set:
SELECT sk.keyword,
CASE WHEN kw.device = 'mobile' THEN 'desktop' ELSE 'mobile' END as device,
kw.rating
FROM
(
SELECT keyword
FROM kw
GROUP BY keyword
HAVING COUNT(*) = 1
)sk
INNER JOIN kw ON kw.keyword = sk.keyword
UNION ALL
SELECT * FROM kw;
As another option that will scale if you add in more 'devices' is to cross join all the potential device/keyword combinations and then left join to your original table:
SELECT
fe.keyword,
fe.device,
CASE WHEN kw.rating IS NULL THEN max(rating) OVER (PARTITION BY fe.keyword) ELSE kw.rating END AS rating
FROM
(
SELECT DISTINCT kw.keyword, kw2.device
FROM kw, kw kw2
) fe
LEFT OUTER JOIN kw ON kw.keyword = fe.keyword
AND kw.device = fe.device;