Selecting Parent Rows With Multiple Conditions - sql

Question

I had most of this query down until a new condition arose and it has confounded me. Given the following simplified table schema:
Parent Table:
ID
FName
LName
Child Table:
[Index]
ParentID
Active_Flag
ExpirationDate
What I want to do is get Parent rows for which:
There are no children.
There are children whose Active_Flag is 1 but whose expiration dates are blank or NULL.
There are indeed children but none have the Active_Flag set to 1.
The following query came up with my first two criteria:
SELECT p.ID, p.LNAME, p.FNAME,
CASE
WHEN COUNT(ct.indx) = 0 THEN 'None'
WHEN ct.ExpirationDate is NULL or ct.ExpirationDate = '' THEN 'No expiration date'
END AS Issue
FROM ParentTable AS p
LEFT JOIN ChildTable ct
ON p.ID = ct.ParentID
GROUP BY p.ID, p.LNAME, p.FNAME, ct.[INDEX], ct.ExpirationDate
HAVING (COUNT(ct.[INDEX]) = 0) OR (ct.ExpirationDate IS NULL OR ct.ExpirationDate = '')
ORDER BY p.LNAME
I don't know how to account for #3. Any help is appreciated. Thanks in advance.

Answer 1

You can also do this in the HAVING clause:
SELECT p.ID, p.LNAME, p.FNAME,
(CASE WHEN COUNT(ct.indx) = 0 THEN 'None'
WHEN ct.ExpirationDate is NULL or ct.ExpirationDate = '' THEN 'No expiration date'
WHEN sum(case when ActiveFlag = 1 then 1 else 0 end) = 0 then 'No active children'
END) AS Issue
FROM ParentTable p LEFT JOIN
ChildTable c
ON p.ID = ct.ParentID
GROUP BY p.ID, p.LNAME, p.FNAME
HAVING (COUNT(ct.[INDEX]) = 0) OR
(ct.ExpirationDate IS NULL OR ct.ExpirationDate = '') or
sum(case when ActiveFlag = 1 then 1 else 0 end) = 0
ORDER BY p.LNAME
The DISTINCT in the SELECT is redundant. You do not need it with an aggregation.
You can simplify the having to "sum(ActiveFlag)" if the activeFlag is indeed an integer. If not, then it should be "= '1'" rather than "= 1'.

Answer 2

you can use unions for this query.....
I am not sure about this query ....but it will help you in solving your prolem
select p.id,p.lname,p.fname from parents where (p.id not in (select pid from children))
union
select p.id,p.lname,p.fname from parents p,children c inner join on c.pid=p.id where c.active_flag=1 and c.expiration_date is null or c.expiration_date=''
union
select p.id,p.lname,p.fname from parents p inner join on c.pid=p.id where c.active_flag<>1;

Answer 3

SELECT *
FROM parenttable pt
-- condition 1: There should be no parents without children at all
WHERE NOT EXISTS (
SELECT * FROM childtable c1
WHERE c1.parent_id = pt.id
)
-- condition 2: There should be no children with a flag but without a date
OR EXISTS (
SELECT * FROM childtable c2
WHERE c2.parent_id = pt.id
AND c2.active_flag = 1 AND c2.expire_date IS NULL
)
-- condition 3: There should at least be a child with the active_flag
OR NOT EXISTS (
SELECT * FROM childtable c3
WHERE c3.parent_id = pt.id
AND c2.active_flag = 1
)
;
-- Active flags for children c1 and c2
-- c1 c2 (X= child doesn't exists)
-----+-----+---+
-- X X rule1+rule3 # no children at all
-- 0 X rule3 # only one child
-- 1 X # idem
-- 0 0 rule 3 # two children
-- 0 1
-- 1 0
-- 1 1
--
-- , which means that rule3 implies rule1, and rule1 is redundant
-------------------------
SELECT *
FROM parenttable pt
-- condition 1+3: There should at least be a child with the active_flag
WHERE NOT EXISTS (
SELECT * FROM childtable c1
WHERE c1.parent_id = pt.id
AND c1.active_flag = 1
)
-- condition 2: There should be no children with a flag but without a date
OR EXISTS (
SELECT * FROM childtable c2
WHERE c2.parent_id = pt.id
AND c2.active_flag = 1 AND c2.expire_date IS NULL
)
;