Problem with several stored values in nvarchar!

Question

Hi everyone,
One friend asked me to help him about a query which needs to join some three tables. There is an nvarchar valued column in the main table that contains several id's need to be joined to another table. For example the value is that '18,20,1,26'. I've found
a query on a simple nvarchar that seperates id's which is on stackoverflow. but when querying there is surely more nvarchar's.
My problem is at that point and I got puzzled: when querying there are much more results rather than single nvarchar. How can I query it?

Answer 1

Some misunderstandings occurred. I want to clear some aspects. That db is a university db. By the time db firstly released, it wasn't thought some problems could happen. That is one of them. I found that query from a site which I mentioned before.
Declare @products varchar(200) = '1|20|3|343|44|6|8765'
Declare @individual varchar(20) = null
WHILE LEN(@products) > 0
BEGIN
IF PATINDEX('%|%',@products) > 0
BEGIN
SET @individual = SUBSTRING(@products, 0, PATINDEX('%|%',@products))
SELECT @individual
SET @products = SUBSTRING(@products, LEN(@individual + '|') + 1,
LEN(@products))
END
ELSE
BEGIN
SET @individual = @products
SET @products = NULL
SELECT @individual
END
END
It can divide the int's in the varchar variable @products.But when querying the real data form db how it can be done? There are some additionals:
we have four tables which are related to each other. In one table there is an nvarchar valued comma seperated data for example '1,15,25,89' which are the id column of another table. But as you can see we need to seperate them  while query is running and
join those values to that "another table". My friend sent me a sample query which gives the following result.
Msg 245, Level 16, State 1, Line 1Conversion failed when converting the nvarchar value '1,2,10,11,12,13,14,15' to data type int.