How do I use a column value in a substrings where clause - sql

Question

03-30 13:17]
I'm trying to use a t-sql against SQL-Server 2005 with asp 3.0. What I want to do is first select all rows that match a certain condition and then I want to know how how many children are connected to that row based on it's ChildID.
This can of course be done by just doing two queries against the db one to get the matching rows for the Parent and one for each row that was found to know how many children have that as Parent.
I have two tables, table1 contains parents and children and table2 contains the information and the id here is ofcourse the id that is saved in parent and children in table1.
Now I want to first find all the children to a certain parent, and in the same sql-statement I want to know how many children is connected to each child.
So Parent 807 has two children, 808 and 809. 808 has 5 children and 809 has 72 children, how can I with one statement get both the information of children 808 and 809 and the numer of children connected to each of them.
My SQL looks like this (gets the children to parent 807)
SELECT Parent, Child, ID, FieldX, FieldY
FROM Tabel1 INNER JOIN Tabel2 ON Parent = ID
WHERE (Parent = 807)
The statement I use to get the numer of children connected to f.ex. 808 is as follows.
SELECT COUNT(*) AS AntalPoster
FROM Tabel1 INNER JOIN Tabel2 ON Child = ID
WHERE (Parent = 808)
What I would like to do is the following, but I would like to substitute the value 808 with the value each record gives me for the child aka SearchID.
SELECT Parent, Child AS SearchID, ID, FieldX, FieldY,
(SELECT COUNT(*) AS [Antal sidor]
FROM Tabel1 INNER JOIN Tabel2 ON Child = ID
WHERE (Parent = 808)) AS AntalPoster
FROM Tabel1 INNER JOIN Tabel2 ON Child = ID
WHERE (Parent = 807)
The problem I get is that "Invalid column name 'SearchID'", what I can understand is that I can't get the value that I find in SerachID to be used as a value in the next SQL-statements where clause.
Is this possible, and if so how?
Thanks in advance.

Answer 1

So, I understand, basically Table1 contains hierarchy information, and Table2 details.
Assuming that, here's my approach:
SELECT
h.Parent,
h.ChCount,
d.* /* you may want to expand it to a specific Table2 column list */
FROM (
/* first, get the children and their child counts */
SELECT
p.Parent,
p.Child,
COUNT(*) AS ChCount
FROM Table1 p
INNER JOIN Table1 c ON p.Child = c.Parent
GROUP BY p.Parent, p.Child
WHERE p.Parent = 807
) h
/* next, get the children's details */
INNER JOIN Table2 d ON h.Child = d.ID

Answer 2

Now I want to first find all the children to a certain parent, and in the same sql-statement I want to know how many children is connected to each child.
This is a way to do that.
declare #Table1 table (Table1ID int, ParentID int)
-- Root
insert into #Table1 values(807, null)
-- Children to 807
insert into #Table1 values(808, 807)
insert into #Table1 values(809, 807)
-- Children to 808
insert into #Table1 values(810, 808)
-- Children to 809
insert into #Table1 values(811, 809)
insert into #Table1 values(812, 809)
select
T1.*,
(select count(*)
from #Table1 as T2
where T1.Table1ID = T2.ParentID) as ChildCount
from #Table1 as T1
where T1.ParentID = 807
Result
Table1ID ParentID ChildCount
----------- ----------- -----------
808 807 1
809 807 2

Answer 3

Replace
WHERE (Parent = SearchID))
by
WHERE (Parent = ParentID))
But you're better of using
SELECT Parent, Child, ID, FieldX, FieldY, COUNT(*) AS AntalPoster
FROM Tabel1 INNER JOIN Tabel2 ON Child = ID
WHERE (Parent = [ParentID])
GROUP
BY Parent, Child, ID, FieldX, FieldY;

Answer 4

If you define a "alias" for a column you can't use this name inside the query earlier than within a group by or order by clause.
As is your example SearchID is just a name for column Child you should use WHERE (PARENT = Child)

Answer 5

You're kinda close.
SELECT Parent_ID, COUNT(*) AS AntalPoster FROM Tabel1 INNER JOIN Tabel2 ON Child = ID
Group by Parent_ID
Now I don' quite understand from reading your question what the 'ID' field is called...but the results of this query should give the Parent_ID along with the count of the number of child records (If I've read your setup corectly). Join to that subquerty to get the count.
SELECT Parent, Child.AntalPoster, ID, FieldX, FieldY
FROM Tabel1 INNER JOIN Tabel2 ON Parent = ID
inner join (SELECT Parent_ID, COUNT(*) AS AntalPoster FROM Tabel1 INNER JOIN Tabel2 ON Child = ID Group by Parent_ID) child on child.id = t1.ID
WHERE (Parent = 807)
Whats really confusing me in your example...if I'm still off with what you're going for...quickly giving us the schema would help. Is the table setup so it has Parent, Child, ID? If so, how does the work? I'd expect Parent_ID, Child_ID...bit confused on the third "ID" column, what does it hold thats unique from the parent,child columns that already exist?.
In any case, the logic is setup a subquery so it reads Key , Count(1). Then join to that subquery on the Key to obtain the count value the subquery returns.