How to output using recursive (parents -> children -> grandchildren) - sql-server

Question

CREATE TABLE PERSON
(
persID INT IDENTITY(1,1) PRIMARY KEY,
persFName VARCHAR(30) NOT NULL,
persLName VARCHAR(30) NOT NULL,
persDOB DATE,
motherID INT FOREIGN KEY REFERENCES person(persID),
fatherID INT FOREIGN KEY REFERENCES person(persID),
persDOD DATE,
persGender CHAR(1),
)
CREATE TABLE COUPLE
(
coupleID INT IDENTITY(1,1) PRIMARY KEY,
alphaSpouse INT NOT NULL FOREIGN KEY REFERENCES person(persID),
omegaSpouse INT NOT NULL FOREIGN KEY REFERENCES person(persID),
coupleStart DATE NOT NULL,
coupleEnd DATE,
)
INSERT INTO person (persFName, persLName, persDOB, motherID, fatherID, persDOD, persGender) VALUES
('Jim', 'Smith', '1920-05-15', NULL, NULL, '2001-04-21','M'),
('Agnes', 'Smith', '1922-09-21', NULL, NULL, '2003-06-01','F'),
('Linda', 'Howard', '1949-03-20', 2, 1, NULL,'F'),
('Helen', 'Bradley', '1942-11-28', 2, 1, NULL,'F'),
('Jim', 'Smith', '1953-02-10', 2, 1, NULL,'M'),
('Stephen', 'Smith', '1957-01-13', 2, 1, '2005-05-25','M'),
('Daniel', 'Smith', '1961-11-28', 2, 1, NULL,'M'),
('Michelle', 'Smith', '1963-07-02', NULL, NULL, NULL,'F'),
('Anne', 'Smith', '1958-04-22', NULL, NULL, NULL,'F'),
('Josh', 'Smith', '1990-01-28', 8, 7, NULL,'M'),
('Stephanie', 'Smith', '1992-05-18', 8, 7, NULL,'F'),
('Rachel', 'Smith', '1996-11-05', 8, 7, NULL,'F'),
('Reg', 'Howard', '1949-07-07', NULL, NULL, NULL,'M'),
('Richard', 'Howard', '1972-12-26', 3, 13, NULL,'M'),
('Phillip', 'Howard', '1975-06-01', 3, 13, NULL,'M'),
('Robert', 'Bradley', '1939-03-07', NULL, NULL, NULL,'M'),
('Matthew', 'Bradley', '1964-10-26', 4, 16, '2001-04-27','M'),
('Yvonne', 'Bradley', '1966-11-28', 4, 16, NULL,'F'),
('James', 'Bradley', '1971-01-26', 4, 16, NULL,'M'),
('Anna', 'Reuper', '1918-01-27', NULL, NULL, NULL,'F'),
('Ludwig', 'Reuper', '1923-07-01', NULL, NULL, '2001-07-01','M'),
('Heinz', 'Reuper', '1965-01-28', 20, 21, NULL,'M'),
('Veronica', 'Reuper', '1959-04-01', 20, 21, NULL,'F'),
('Marco', 'Johnson', '1958-09-04', NULL, NULL, NULL,'M'),
('Francesca', 'Reuper', '1990-11-01', 23, 24, NULL,'F'),
('Lou', 'Jung', '1940-02-03', NULL, NULL, NULL,'M'),
('Tammi', 'Sinclair', '1971-02-03', NULL, NULL, NULL,'F'),
('Lori', 'Navarro', '1973-12-15', NULL, NULL, NULL,'F'),
('Kattie', 'Paine', '1980-10-31', NULL, NULL, NULL,'F');
INSERT INTO couple (alphaSpouse,omegaSpouse, coupleStart, coupleEnd) VALUES
(1,2,'1940-05-22', NULL),
(3,13,'1969-07-30', '1973-10-01'),
(3,26,'1980-01-10', '1982-12-01'),
(4,16,'1963-04-05', NULL),
(6,9,'1979-06-21', NULL),
(7,8,'1987-09-14', NULL),
(20,21,'1936-10-26', NULL),
(23,24,'1988-05-01', '1997-07-01'),
(19,27,'1992-10-31', '1993-01-31'),
(19,28,'1995-08-18', '1997-04-27'),
(19,29,'2015-09-19', NULL);
I'm trying to list all the people who have grandchildren and how many grandchildren they each have. I'd like an ouput like this;
I attempted to do it below, but I got stuck trying to COUNT grandkids outside the WHERE subquery.. was I even on the right track?
SELECT grandp.persFName + ' ' + grandp.persLName, COUNT(grandkids.persID)
FROM person grandp
JOIN person child ON grandp.persID = child.motherID OR grandp.persID = child.fatherID
WHERE child.persID IN (SELECT grandkids.motherID
FROM person grandkids
union
SELECT grandkids.fatherID
FROM person grandkids)
GROUP BY grandp.persFName + ' ' + grandp.persLName

Answer 1

When you have hierarchical data like yours, it's best approached with common table expressions. This will allow you to build the hierarchical data into a form that you can later use - in your example, to count grandchildren. You can take advantage of building data by levels or distance from the root.
with temp (persid, ancestorid, level) as (
select persid, persid as ancestorid, 0 as level
from person
where motherid is null and fatherid is null
union all
select person.persid, temp.ancestorid, temp.level + 1 as level
from person
inner join temp on temp.persid = person.motherid or temp.persid = person.fatherid
)
select temp.ancestorid as persid,
person.persFName + ' ' + person.persLName as name,
count(*)
from temp
inner join person
on temp.ancestorid = person.persid
where level = 2
group by temp.ancestorid, person.persFName, person.persLName
The query builds a CTE of each person, it's ancestor and the level (0 = grandparents, 2 = grandchildren). You can then easily count grandchildren for each ancestor.
SQL Fiddle: http://sqlfiddle.com/#!3/99c97/2
(Note: I left the couple table out as it's not needed here).

Answer 2

Try this I just used common table expressions recursively to get the result
;WITH Allpersons AS
(
SELECT persID AS Id
,persFName+' '+persLName AS Name
,fatherID
,motherID
FROM PERSON
)
SELECT
GrandFatherCTE.Name
,COUNT(GrandFatherCTE.Id ) AS CountOfChild
FROM Allpersons AllPersonsCTE
INNER JOIN
Allpersons ParentsCte
ON
AllPersonsCTE.fatherID = ParentsCte.Id
OR
AllPersonsCTE.motherID = ParentsCte.Id
INNER JOIN
Allpersons GrandFatherCTE
ON
ParentsCte.fatherID = GrandFatherCTE.Id
OR
ParentsCte.motherID = GrandFatherCTE.Id
INNER JOIN
COUPLE
ON
GrandFatherCTE.Id = COUPLE.alphaSpouse
OR
GrandFatherCTE.Id = COUPLE.omegaSpouse
GROUP BY
GrandFatherCTE.Name
,COUPLE.coupleID
ORDER BY
CountOfChild ASC
,COUPLE.coupleID ASC