SQL query with GROUP BY and HAVING - sql

Question

I have a little problem in mi project, i'm trying to make a query on a single table but I'm not succeeding.
The table is this:
CREATE TABLE PARTITA(
COD_SFIDA VARCHAR (20) PRIMARY KEY,
DATA_P DATE NOT NULL,
RISULTATO CHAR (3) NOT NULL,
COD_DECK_IC VARCHAR (15),
COD_DECK_FC VARCHAR (15),
COD_EVT VARCHAR (15),
TAG_USR_IC VARCHAR (15),
TAG_USR_FC VARCHAR (15),
CONSTRAINT CHECK_RISULTATO CHECK (RISULTATO='0-0' OR RISULTATO='0-1' OR RISULTATO='1-0' OR RISULTATO='1-1'),
CONSTRAINT FK8 FOREIGN KEY (COD_DECK_IC, TAG_USR_IC) REFERENCES DECK (COD_DECK, TAG_USR) ON DELETE CASCADE,
CONSTRAINT FK17 FOREIGN KEY (COD_DECK_FC, TAG_USR_FC) REFERENCES DECK (COD_DECK, TAG_USR) ON DELETE CASCADE,
CONSTRAINT FK9 FOREIGN KEY (COD_EVT) REFERENCES TORNEO (COD_EVENTO) ON DELETE CASCADE
);
I would like to view the most used deck by each user.
this is the query I tried to do:
SELECT P.COD_DECK_FC, P.TAG_USR_FC, COUNT(P.COD_DECK_FC)
FROM PARTITA P
GROUP BY P.TAG_USR_FC, P.COD_DECK_FC
UNION
SELECT P.COD_DECK_IC, P.TAG_USR_IC, COUNT(P.COD_DECK_IC)
FROM PARTITA P
GROUP BY P.TAG_USR_IC, P.COD_DECK_IC
/
But I would like to view just the most used deck by each user and don't all the decks and how many times users used them.
How can I do?
I would like the query to show the tag_usr and the cod_deck that is used the most for all of this for each user
eg:
cod_deck tag_usr count(cod_deck)
------------- ----------- --------------
1 A1BE2 5
2 AE3NF 6
5 FNKJD 3
instead the previious query returns to me:
cod_deck tag_usr count(cod_deck)
------------- ----------- --------------
1 A1BE2 5
2 AE3NF 6
5 FNKJD 3
2 A1BE2 2
1 AE3NF 3
I just want that the query show me the users A1BE2 and AE3NF just one time, because the query have to select the most used deck of each user.

Answer 1

You don't want to select a field that you're counting. Try something like this:
SELECT P.COD_DECK_FC, P.TAG_USR_FC, COUNT(P.COD_SFIDA)
FROM PARTITA P
GROUP BY P.COD_DECK_FC, P.TAG_USR_FC
UNION
SELECT P.COD_DECK_IC, P.TAG_USR_IC, COUNT(P.COD_SFIDA)
FROM PARTITA P
GROUP BY P.COD_DECK_IC, P.TAG_USR_IC
That will list all of the combinations of COD_DECK_FC and TAG_USR_FC
and then number of times it appears in the table, and then do the same with COD_DECK_IC and TAG_USR_IC. It's not clear to me from your question exactly what you want, but I know that you shouldn't put a field in COUNT if you're selecting it.

Answer 2

If i understand correctly you need subquery with ranking function :
with t as (
select *, row_number() over (partition by cod_deck order by count desc) Seq
from (<union query>)
)
select *
from cte c
where seq = 1;

Answer 3

I think you want this:
with ct as (
select P.COD_DECK_FC as deck, P.TAG_USR_FC as usr, COUNT(P.COD_DECK_FC) as cnt
from partita p
group by P.TAG_USR_FC, P.COD_DECK_FC
union all
select P.COD_DECK_IC, P.TAG_USR_IC, COUNT(P.COD_DECK_IC)
from partita P
group by P.TAG_USR_IC, P.COD_DECK_IC
)
select ct.*
from (select ct.*,
row_number() over (partition by usr order by cnt desc) as seqnum
from ct
) ct
where seqnum = 1;
You can also shorten this using grouping sets:
select p.*
from (select coalesce(P.COD_DECK_FC, P.COD_DECK_IC) as deck,
coalesce(P.TAG_USR_FC, P.TAG_USR_IC) as usr,
count(*) as cnt,
row_number() over (partition by coalesce(P.TAG_USR_FC, P.TAG_USR_IC) order by count(*) desc) as seqnum
from partita p
group by grouping sets ( (P.TAG_USR_FC, P.COD_DECK_FC), P.TAG_USR_IC, P.COD_DECK_IC) )
) p
where seqnum = 1;