SQL: Multiple select statements in one query - sql

Question

I want to select information from three SQL tables within one query.
An example could be the following setup.
tblFriends
id | idmother | dayBirth
--------------------------
1 | 1 | 09/09/21
2 | 2 | 09/09/21
3 | 3 | 11/09/21
4 | 3 | 11/09/21
5 | 4 | 07/09/21
... | ... | ...
tblMothers
id | name
---------------
1 | Alice
2 | Samantha
3 | Veronica
4 | Maria
... | ...
tblIsAssignedParty
idMother | codeParty | price
------------------------------
1 | 231 | 15
2 | 645 | 28
3 | 164 | 33
... | ... | ...
I want to have a query that gives me the following:
dayBirth | weekDay | totalFriendsForParty | totalFriendsForPartyPercent | totalFriendsNoParty | totalFriendsNoPartyPercent
-----------------------------------------------------------------------------------------------------------------------------
07/09/21 | Tuesday | 0 | 0 | 1 | 0.??
09/09/21 | Thursday | 2 | 0.?? | 0 | 0
11/09/21 | Saturday | 2 | 0.?? | 0 | 0
Note:
dayBirth = simply the day of birth; I need the friends grouped by this date
weekDay = dayBirth name
totalFriendsForParty = friends who will be attending the party; we know if the mother has a party assigned
totalFriendsForPartyPercent = Percentatge of friends, of the total number of friends who will attend the parties
totalFriendsNoParty = friends who will not attend the party; we know if the mother does not have a party assigned
totalFriendsNoPartyPercent = Percentatge of friends, of the total number of friends who will not attend the parties
I need the number of friends based on whether their mothers are at a party or not. I tried to multiple select statements in Single query but the following code didn't work:
SELECT
(SELECT distinct dayBirth, TO_CHAR(dayBirth, 'DAY') from tblFriends) as firstSecondColumn,
(SELECT dayBirth, count(*) from tblFriends
where idMother IN (
SELECT f.idMother
from tblFriends f
left join tblIsAssignedParty iap
on f.idMother = iap.idMother
where iap.codeParty is not null)
group by dayBirth) as thirdColumn,
(SELECT TRUNC(count(*) / count(thirdColumn.id) , 2) from tblFriends) as quarterColumn,
(SELECT dayBirth, count(*) from tblFriends
where idMother IN (
SELECT f.idMother
from tblFriends f
left join tblIsAssignedParty iap
on f.idMother = iap.idMother
where iap.codeParty is not null)
group by dayBirth) as fifthColumn,
(SELECT TRUNC(count(*) / count(fifthColumn.id) , 2) from tblFriends) as sixthColumn,
order by dayBirth
Any advice on this one? I try to learn, I do what I can :-(
Edit: I can't add inserts because it's a file upload, but I can add an approximation of table creation.
Create tables:
CREATE TABLE tblFriends
(
id NUMBER(*,0),
idMother CHAR(10 CHAR),
CONSTRAINT PK_FRIEND PRIMARY KEY (id, idMother),
CONSTRAINT FK_IDMOTHER FOREIGN KEY (idMother)
REFERENCES tblMothers (id),
dayBirth DATE CONSTRAINT NN_DAY NOT NULL
)
CREATE TABLE tblMothers
(
id CHAR(10 CHAR) CONSTRAINT PK_MOTHER PRIMARY KEY (id),
name VARCHAR2(20 CHAR) CONSTRAINT NN_MNAME NOT NULL
)
CREATE TABLE tblIsAssignedParty
(
idMother CHAR(10 CHAR),
codeParty CHAR(10 CHAR),
CONSTRAINT PK_ASSIGNED PRIMARY KEY (idMother, codeParty),
CONSTRAINT FK_ASSIGNEDMOTHER FOREIGN KEY (idMother)
REFERENCES tblMothers (id),
CONSTRAINT FK_ASSIGNEDPARTY FOREIGN KEY (codeParty)
REFERENCES tblParties (codeParty),
price DECIMAL(10,2)
)

Answer 1

You appear to want to LEFT JOIN the firends and party tables and then use conditional aggregation:
SELECT dayBirth,
TO_CHAR(dayBirth, 'FMDAY', 'NLS_DATE_LANGUAGE=English') AS day,
COUNT(p.idmother)
AS totalFriendsForParty,
COUNT(p.idmother) / COUNT(*) * 100
AS totalFriendsForPartyPercent,
COUNT(CASE WHEN p.idmother IS NULL THEN 1 END) AS totalFriendsNoParty,
COUNT(CASE WHEN p.idmother IS NULL THEN 1 END) / COUNT(*) * 100
AS totalFriendsNoPartyPercent
FROM tblFriends f
LEFT OUTER JOIN tblIsAssignedParty p
ON (f.idmother = p.idmother)
GROUP BY dayBirth
Which, for the sample data:
CREATE TABLE tblFriends (id, idmother, dayBirth) AS
SELECT 1, 1, DATE '2021-09-09' FROM DUAL UNION ALL
SELECT 2, 2, DATE '2021-09-09' FROM DUAL UNION ALL
SELECT 3, 3, DATE '2021-09-11' FROM DUAL UNION ALL
SELECT 4, 3, DATE '2021-09-11' FROM DUAL UNION ALL
SELECT 5, 4, DATE '2021-09-07' FROM DUAL;
CREATE TABLE tblIsAssignedParty (idMother, codeParty, price) AS
SELECT 1, 231, 15 FROM DUAL UNION ALL
SELECT 2, 645, 28 FROM DUAL UNION ALL
SELECT 3, 164, 33 FROM DUAL;
Outputs:
DAYBIRTH
DAY
TOTALFRIENDSFORPARTY
TOTALFRIENDSFORPARTYPERCENT
TOTALFRIENDSNOPARTY
TOTALFRIENDSNOPARTYPERCENT
09-SEP-21
THURSDAY
2
100
0
0
11-SEP-21
SATURDAY
2
100
0
0
07-SEP-21
TUESDAY
0
0
1
100
db<>fiddle here