SQL Server CTE use IDs from single column with EXCEPT? - sql

Question

Having received kindness the other day from someone whose eyes were less bleary than mine I thought I'd give it another shot. Thanks in advance for your assistance.
I have a single SQL Server (2012) table named Contacts. That table has four columns I am currently concerned with. The table has a total of 71,454 rows. There are two types of records in the table; Companies and Employees. Both use the same column, named (Client ID), for their primary key. The existence of a Company Name is what differentiates between Company and Employee data. Employees have no associated Company Name. There are 29,021 Companies leaving 42,433 Employees.
There may be 0-n number of Employees associated with any one Company. I am attempting to create output that will reflect the relationship between Companies and Clients, if there are any. I would like to use the Company ID (Client ID column) as my anchor data set.
Not sure my definition is correct but the thought was to create a CTE of the known Companies by virtue of a given Company Name. Then, use the remaining Client IDs but use the EXCEPT clause to filter the already-retrieved Client IDs out of the result set.
Here the code I currently have;
;
WITH cte ( BaseID, Client_id, Company_name,
First_name, Last_name, [level] )
AS ( SELECT Client_id AS BaseID ,
Client_id ,
Company_name ,
First_name ,
Last_name ,
1
FROM dbo.Conv_client_clean
WHERE ( COMPANY_NAME IS NOT NULL
OR COMPANY_NAME != ''
)
UNION ALL
SELECT c.BaseID ,
children.Client_id ,
children.Company_name ,
children.First_name ,
children.Last_name ,
cte.[level] + 1
FROM dbo.Conv_client_clean children
INNER JOIN cte c ON c.Client_id = children.CLIENT_ID
EXCEPT
SELECT children.Client_id
FROM cte
)
SELECT BaseID ,
Client_id ,
Company_name ,
first_name ,
Last_name ,
[Level]
FROM cte
OPTION ( MAXRECURSION 0 );
In this instance I receive the following error;
Msg 252, Level 16, State 1, Line 3
Recursive common table expression 'cte' does not contain a top-level UNION ALL operator.
Any suggestions?
Thanks!

Answer 1

In the recursion cte query, you cannot have more set operations(union, except, union all,intersect) after the the one Union ALL which is refers the cte itself. I think what you can try is change the query as below and check
...
UNION ALL
SELECT c.BaseID ,
children.Client_id ,
children.Company_name ,
children.First_name ,
children.Last_name ,
cte.[level] + 1
FROM dbo.Conv_client_clean children
WHERE children.Client_id NOT IN (SELECT Client_id FROM cte)

Answer 2

As mentioned to Kiran I was able to concoct an 'old fashioned' approach what is good enough for now.
Thank you everyone for your kind attention.

Answer 3

I'm not sure what you are trying to do with level. It seems that it will be 1 for companies and 2 for employees. If that's the case, you don't even need recursion. The first part of your cte creates a list of companies. That's fine. Now use that to join back to the original table to show all the employees too.
WITH
cte( BaseID, ClientID, Company_name, First_name, Last_name )AS(
SELECT Base_ID,
Base_ID AS Client_id ,
Company_name,
First_name,
Last_name
FROM dbo.Conv_client_clean
WHERE COMPANY_NAME IS NOT NULL
OR COMPANY_NAME <> ''
)
select c2.Base_id, c2.Client_id,
c1.Company_Name, c2.First_Name, c2.Last_Name,
case when c2.client_id is null then 1 else 2 end Level
from cte c1
join Conv_client_clean c2
on c1.BaseID = isnull( c2.Client_ID, c2.Base_id )
order by c1.BaseID, c2.Base_id;
Here's where I fiddled with it.

Answer 4

Unfortunately anything besides UNION ALL, after you've made your recursive reference, will not work. And if you think about it, it makes sense.
Recursion is conceptually identical to the following where recursion continues until max depth is reached or a query returns no results upon which another execution could act.
WITH Anchor AS (select...)
,recurse1 as (<Some body referring to Anchor>)
,recurse2 as (<Identical body except referring to recurse1>)
,recurse3 as (<Identical body except referring to recurse2>)
...
select * from Anchor
union all
select * from recurse1
union all
select * from recurse2
...
The problem is that conjunctive operators apply to EVERYTHING that precedes it. In your case, EXCEPT operates on everything to it's left side which includes the Anchor query. Afterwards, when looking for the anchor to which the recursive part must be applied, the query compiler doesn't find a 'top level union all operator' any more because it's been consumed as part of the left side of your recursive query.
It wouldn't help to contrive some syntax akin to parenthesis that could delimit the scope of the left side of your table conjunction because you would then build a case of 'multiple recursive references' which is also illegal.
BOTTOM LINE IS: The only conjunction that works in the recursive part of your query is UNION ALL because it simply concatenates the right side. It doesn't require knowledge of the left side to determine which rows to include.