Update using join and group with count - mysql

Question

I am able to do an update between tables based on a count in the second table like so:
Update TableJ J
Inner Join (Select B_ID,C,S from TableC group by C,S having count=1) C
On J.C=C.C and J.S=C.S
Set T1.B_ID=T2.B_ID
The problem is my TableC does not contain S, that is stored in another table and related via B call it Table_BS (no jokes please :| ). If I didn't have to worry about count therefore I could do:
Update TableJ J
Inner Join TableC C
Inner Join TableBS BS
On J.C=C.C and C.S=BS.S
Set J.B_ID=BS.B_ID
Except the issue is, as with the original count, I only want to return B_ID when there is only one C record with an S record in TableBS.
Update:
Well this is how far I've gotten (select wise):
Select J.ID,B.B_ID
From DBJ J Inner Join LBS B Inner Join C
On J.C=C.C And (
J.S_ID = B.S_ID
or J.S_ID=B.CS_ID)
and B.B_ID=C.B_ID
Which in my case returns three records:
+----+------+
| ID | B_ID |
+----+------+
| 88 | 100 |
+----+------+
| 90 | 200 |
+----+------+
| 90 | 200 |
+----+------+
ID being the record I want to update, B_ID being the value I want to update with. In this case it turns out the count I am trying to limit is the ID column in the output, in other words I only want to update TableJ, record 88 with the value 100. TableJ record 90 turns out to have >1 result so I want to skip it. Just not sure where to put the group by or count here.
Update: Not sure why this solution remains just outside my grasp though getting closer, I can get the select to now return the ID of the record to update and the value to update with only on those records with one result like so:
Select J.ID,B.B_ID
From DBJ J Inner Join LBS B Inner Join C
On J.C=C.C And (
J.S_ID = B.S_ID
or J.S_ID=B.CS_ID)
and B.B_ID=C.B_ID group by J.ID having count(*)=1
which returns
+----+------+
| ID | B_ID |
+----+------+
| 88 | 100 |
+----+------+
And still unable to now get that to update TableJ record 88 field B_ID with the value of 100.

Answer 1

I am not sure if I understood correctly the problem,but here is my solution
Update TableJ J
Inner Join (
Select B_ID,TableC.C, TableBS.S
from TableC Inner Join TableBS
on TableC.B= TableBS.B
group by TableC.C,TableBS.S
having count(*)=1
) C
On J.C=C.C
Set J.B_ID=C.B_ID

Answer 2

This seems to have done the trick so far:
Update TableJ T1
Inner Join
(Select J.ID,B.B_ID
From TableJ J Inner Join TableBS B Inner Join TableC C
On J.C=C.C
And J.S = B.S
And B.B_ID=C.B_ID
group by J.ID having count(*)=1) T2
On T1.ID=T2.ID Set T1.B_ID=T2.B_ID
Basically solved it first with a select that returned the ID of the Update TableJ and the B_ID from TableBS where the C in TableC matched the C in TableJ and the S in TableBS matched the S in TableJ. I did a count on the results based on the ID in TableJ so that I only returned values when I got one result.