Fetch data from one table and insert into two tables in desired format

Question

I have similar to the following data in a table and it is not normalized. The groupID is being used to group two records of similar nature.
DECLARE @OldDoc TABLE (oldDocID INT, groupID INT, deptID INT)
INSERT INTO @OldDoc (oldDocID, groupID) VALUES (1, NULL, 111),(2,NULL,111),(3,1,111),(4,NULL,333),(5,1,222),(6,NULL,333),(7,2,222),(8,2,333),(9,NULL,111),(10,3,222),(11,NULL,333),(12,3,444)
I need to process the data from the above table (@OldDoc) and write into two new tables (@NewDoc and @NewDocGroup) as follows.
oldDocID should be stored as newDocID when inserting to @NewDoc table. Only records with groupID NULL and one record (first one) per group should be considered (For example, oldDocID 5 is not considered as 3 and 5 belong to the same groupID 1) for insertion. 
DECLARE @NewDoc TABLE (newDocID INT)
INSERT INTO @NewDoc (newDocID) VALUES (1),(2),(3),(4),(6),(7),(9),(10),(11)
All records from @OldDoc should be considered for insertion into @NewDocGroup table. OldDocID is inserted as NewDocID and deptID is as-is. Instead of groupID, the ID of the first record in the 
group should be considered as parentNewDocID (For example, 3 is considered as parentNewDocID for newDocID 5 as 3 and 5 belong to the same groupID in @OldDoc table) for the newDocID.
DECLARE @NewDocGroup (newDocID INT, parentNewDocID INT, deptID INT)
INSERT INTO @NewDocGroup (newDocID, parentNewDocID, deptID) VALUES (1,1,111),(2,2,111),(3,3,111),(4,4,333),(5,3,222),(6,6,333),(7,7,222),(8,7,333),(9,9,111),(10,10,222),(11,11,333),(12,10,444)
How do I accomplish the above using SQL ? Thanks for the help.

Answer 1

>> I have similar to the following data in a table and it is not normalized. The group_id is being used to group two records [sic] of similar nature. <<
Rows are not records. Tables have to have a key by definition. You do not do math with identifiers, so they should not be numeric. Let's ignore that error for now. In short, you are posting garbage. If you had followed Forum Netiquette, would you have posted
this? 
CREATE TABLE Old_Documents
(old_doc_id INTEGER NOT NULL PRIMARY KEY, 
 group_id INTEGER, 
 dept_nbr INTEGER NOT NULL
   REFERENCES Departments (dept_nbr));
INSERT INTO Old_Documents(old_doc_id, group_id, dept_nbr) 
VALUES  (1, NULL, 111), 
(2, NULL, 111), 
(3, 1, 111), 
(4, NULL, 333), 
(5, 1, 222), 
(6, NULL, 333), 
(7, 2, 222), 
(8, 2, 333), 
(9, NULL, 111), 
(10, 3, 222), 
(11, NULL, 333), 
(12, 3, 444);
>> I need to process the data from the above table (Old_Documents) and write into two new tables (New_Documents and New_Documents_Groups) as follows. <<
Just like punch cards and mag tape data processing! Being old and being new are a status, not another kind of entity. But that is how mag tapes work. And you even use the verb "fetch" from tape files. This design flaw is called  attribute splitting.
Do you have a Male_Personnel and Female_Personnel table? NO! It is just Personnel! 
>> old_doc_id should be stored as new_doc_id when inserting to New_Documents table. Only records [sic] with group_id NULL and one record [sic] (first [sic; no ordering in a table] one) per group should be considered (For example, old_doc_id 5 is not considered
as 3 and 5 belong to the same group_id =1) for insertion. <<
Think about your punch card mindset. Why did you physically materialize that redundant New_Documents table? Let me answer that: this is how you work with punch cards! In SQL we use a VIEW:
CREATE VIEW New_Documents (new_doc_id)
AS 
SELECT old_doc_id 
  FROM Old_Documents;
>> All records [sic] from Old_Documents should be considered for insertion into New_Documents_Groups table. The old_doc_id is inserted as new_doc_id and dept_nbr is as-is. Instead of group_id, the ID [sic: which identifier??] of the first [sic: tables
have no ordering like a deck of punch cards] record [sic] in the group should be considered as parent_new_doc_id (For example, 3 is considered as parent_new_doc_id for new_doc_id 5 as 3 and 5 belong to the same group_id in Old_Documents table) for the new_doc_id.
<<
Why not use 5 as the parent? My guess is that you are trying to form equivalence classes. See:
https://www.simple-talk.com/content/print.aspx?article=2020
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