Making a conditional aggregate - sql

Question

I have tricky grouping problem for our business reasons, I have a table which has values like this
----------------------------
| NAME | TYPE | VALUE |
----------------------------
| N1 | T1 | V1 |
| N1 | T2 | V2 |
| N1 | NULL | V3 |
| N2 | T2 | V4 |
| N2 | NULL | V5 |
| N3 | NULL | V6 |
-----------------------------
I need to group it in a way that,
The first level grouping will be by name.
At the second level,
When the available types are T1,T2 and NULL, group T1 and NULL together and have T2 grouped seperately.
When the available types are T2 and NULL, group NULL with T2.
When NULL is the only available type, just have it as it is.
The expected O/P for the above table is,
----------------------------
| N1 | T1 | V1+V3 |
| N1 | T2 | V2 |
| N2 | T2 | V4+V5 |
| N3 | NULL | V6 |
-----------------------------
How to achieve this in snowflake sql. Or any other server, so that I can find an equivalent in Snowflake.

Answer 1

The following query should work:
SELECT t1.NAME, COALESCE(TYPE, MIN_TYPE), SUM(VALUE)
FROM mytable AS t1
JOIN (
SELECT NAME, MIN(TYPE) AS MIN_TYPE
FROM mytable
GROUP BY NAME
) AS t2 ON t1.NAME = t2.NAME
GROUP BY t1.NAME, COALESCE(TYPE, MIN_TYPE)
The query uses a derived table in order to extract the MIN(TYPE) value per NAME. Using COALESCE we can then convert NULL to either T1 or T2.
Edit:
You can create a pivoted version of the expected result set using the following query:
SELECT NAME,
CASE
WHEN T1SUM IS NULL THEN 0
ELSE COALESCE(T1SUM, 0) + COALESCE(NULLSUM,0)
END AS T1SUM,
CASE
WHEN T1SUM IS NULL AND T2SUM IS NOT NULL
THEN COALESCE(T2SUM, 0) + COALESCE(NULLSUM,0)
ELSE COALESCE(T2SUM, 0)
END AS T2SUM,
CASE
WHEN T1SUM IS NULL AND T2SUM IS NULL THEN COALESCE(NULLSUM,0)
ELSE 0
END AS NULLSUM
FROM (
SELECT NAME,
SUM(CASE WHEN TYPE = 'T1' THEN VALUE END) AS T1SUM,
SUM(CASE WHEN TYPE = 'T2' THEN VALUE END) AS T2SUM,
SUM(CASE WHEN TYPE IS NULL THEN VALUE END) AS NULLSUM
FROM mytable
GROUP BY NAME) AS t

Answer 2

So in Giorgos's answer that totals are given in a pivoted, or single row be case form, not many rows per case, and this can be written simpler:
with this data:
WITH data_table(name, type, value) AS (
SELECT * FROM VALUES
(10, 1, 100 ),
(10, 2, 200 ),
(10, null, 400 ),
(11, 2, 100 ),
(11, null, 200 ),
(12, null, 100 )
)
and this SQL
SELECT name
,SUM(IFF(type=1, value, null)) as t1_val
,SUM(IFF(type=2, value, null)) as t2_val
,SUM(IFF(type is null, value, null)) as tnull_val
,IFF(t1_val is not null, t1_val + zeroifnull(tnull_val), null) as c1_sum
,IFF(t1_val is not null, t2_val, t2_val + zeroifnull(tnull_val)) as c2_sum
,IFF(t1_val is null AND t2_val is null, tnull_val, null) as c3_sum
FROM data_table
GROUP BY 1;
we get:
NAME
T1_VAL
T2_VAL
TNULL_VAL
C1_SUM
C2_SUM
C3_SUM
10
100
200
400
500
200
null
11
null
100
200
null
300
null
12
null
null
100
null
null
100
which shows for the 10 row the null sum binds with 1 sum, for the 11 row the null sum binds with the 2 sum, and in the 12 row we get the null sum by itself.
We can unpivot these values if we wish, but joining to a mini table with 3 rows like so:
SELECT d.name,
p.c2 as type,
case p.c1
WHEN 1 then d.c1_sum
WHEN 2 then d.c2_sum
ELSE d.c3_sum
end as value
FROM (
SELECT name
,SUM(IFF(type=1, value, null)) as t1_val
,SUM(IFF(type=2, value, null)) as t2_val
,SUM(IFF(type is null, value, null)) as tnull_val
,IFF(t1_val is not null, t1_val + zeroifnull(tnull_val), null) as c1_sum
,IFF(t1_val is not null, t2_val, t2_val + zeroifnull(tnull_val)) as c2_sum
,IFF(t1_val is null AND t2_val is null, tnull_val, null) as c3_sum
FROM data_table
GROUP BY 1
) AS d
JOIN (
SELECT column1 as c1, column2 as c2
FROM VALUES (1,'T1'),(2,'T2'),(null,'null')
) AS p
ON ((d.c1_sum is not null AND p.c1 = 1)
OR (d.c2_sum is not null AND p.c1 = 2)
OR (d.c3_sum is not null AND p.c1 is null))
ORDER BY 1,2;
which gives the original requested output:
NAME
TYPE
VALUE
10
T1
500
10
T2
200
11
T2
300
12
null
100