Database schema:
CREATE TABLE Document_Subsets (
  Document_Subset_ID NUMBER PRIMARY KEY,
  Document_Subset_Name TEXT,
  Document_Subset_Details TEXT
);
CREATE TABLE Collection_Subsets (
  Collection_Subset_ID NUMBER PRIMARY KEY,
  Collection_Subset_Name TEXT,
  Collecrtion_Subset_Details TEXT
);
CREATE TABLE Document_Objects (
  Document_Object_ID NUMBER PRIMARY KEY,
  Parent_Document_Object_ID NUMBER,
  Owner TEXT,
  Description TEXT,
  Other_Details TEXT
);
CREATE TABLE Collections (
  Collection_ID NUMBER PRIMARY KEY,
  Parent_Collection_ID NUMBER,
  Collection_Name TEXT,
  Collection_Description TEXT
);
CREATE TABLE Documents_in_Collections (
  Document_Object_ID NUMBER PRIMARY KEY,
  Collection_ID NUMBER,
  FOREIGN KEY (Collection_ID) REFERENCES Collections(Collection_ID),
  FOREIGN KEY (Document_Object_ID) REFERENCES Document_Objects(Document_Object_ID)
);
CREATE TABLE Document_Subset_Members (
  Document_Object_ID NUMBER PRIMARY KEY,
  Related_Document_Object_ID NUMBER,
  Document_Subset_ID NUMBER,
  FOREIGN KEY (Document_Subset_ID) REFERENCES Document_Subsets(Document_Subset_ID),
  FOREIGN KEY (Related_Document_Object_ID) REFERENCES Document_Objects(Document_Object_ID),
  FOREIGN KEY (Document_Object_ID) REFERENCES Document_Objects(Document_Object_ID)
);
CREATE TABLE Collection_Subset_Members (
  Collection_ID NUMBER PRIMARY KEY,
  Related_Collection_ID NUMBER,
  Collection_Subset_ID NUMBER,
  FOREIGN KEY (Collection_Subset_ID) REFERENCES Collection_Subsets(Collection_Subset_ID),
  FOREIGN KEY (Related_Collection_ID) REFERENCES Collections(Collection_ID),
  FOREIGN KEY (Collection_ID) REFERENCES Collections(Collection_ID)
);

Question: What is the owner of the parent document of document owned by 'Marlin'?
SQL: SELECT T2.Owner FROM Document_Objects AS T1 JOIN Document_Objects AS T2 ON T1.Parent_Document_Object_ID = T2.Document_Object_ID WHERE T1.Owner  =  'Marlin'

Question: What are the ids of the documents that are not parent documents?
SQL: SELECT Document_Object_ID FROM Document_Objects EXCEPT SELECT Parent_Document_Object_ID FROM Document_Objects

Question: Which collection have most number of documents? List collection name, id and number of documents.
SQL: SELECT T1.Collection_Name ,  T1.Collection_ID ,  count(*) FROM Collections AS T1 JOIN Documents_in_Collections AS T2 ON T1.Collection_ID = T2.Collection_ID WHERE T1.Collection_Name = "Best" GROUP BY T1.Collection_ID ORDER BY count(*) DESC LIMIT 1;

Question: What are the names of all parent collections of the collection named Nice?
SQL: SELECT T2.Collection_Name FROM Collections AS T1 JOIN Collections AS T2 ON T1.Parent_Collection_ID = T2.Collection_ID WHERE T1.Collection_Name = "Nice";

Question: How many documents does collection named 'Best' has?
SQL: SELECT count(*) FROM Collections AS T1 JOIN Documents_in_Collections AS T2 ON T1.Collection_ID = T2.Collection_ID WHERE T1.Collection_Name = "Best";

Question: Which collection subset does collection name Best in? List collection subset name.
SQL: SELECT DISTINCT T1.Collection_Subset_Name FROM Collection_Subsets AS T1 JOIN Collection_Subset_Members AS T2 ON T1.Collection_Subset_ID =  T2.Collection_Subset_ID JOIN Collections AS T3 ON T2.Collection_ID =  T3.Collection_ID WHERE T3.Collection_Name = "Best";

Question: List id of documents that in document subset Best for 2000 or in collection named Best.
SQL: SELECT DISTINCT T1.Document_Object_ID FROM Document_Subset_Members AS T1 JOIN Document_Subsets AS T2 ON T1.Document_Subset_ID =  T2.Document_Subset_ID JOIN Documents_in_Collections AS T3 ON T1.Document_Object_ID  =  T3.Document_Object_ID JOIN Collections AS T4 ON T3.Collection_ID  =  T4.Collection_ID WHERE T2.Document_Subset_Name = "Best for 2000" OR T4.Collection_Name = "Best";

Question: For document subset named 'Best for 2000', List all document id that in this subset.
SQL: SELECT DISTINCT T1.Document_Object_ID FROM Document_Subset_Members AS T1 JOIN Document_Subsets AS T2 ON T1.Document_Subset_ID =  T2.Document_Subset_ID WHERE T2.Document_Subset_Name = "Best for 2000";

Question: What are the different owners of documents that are related to ones owned by Braeden?
SQL: SELECT DISTINCT OWNER FROM Document_Subset_Members AS T1 JOIN Document_Objects AS T2 ON T1.Related_Document_Object_ID  =  T2.Document_Object_ID WHERE T2.Owner  =  'Braeden';

Question: What are the ids of the dcouments that have between 2 and 4 related documents and how many related items are there?
SQL: SELECT Document_Object_ID , count(*) FROM Document_Subset_Members GROUP BY Document_Object_ID HAVING count(*) BETWEEN 2 AND 4;

Question: What are the details on the document subsets that are named 'Best for 2000'?
SQL: SELECT Document_Subset_Details FROM Document_Subsets WHERE Document_Subset_Name = "Best for 2000";

Question: What is the parent document of document owned by Marlin? List the document id.
SQL: SELECT Parent_Document_Object_ID FROM Document_Objects WHERE OWNER  =  'Marlin'

Question: What are the document object ids of the related to the document owned by Ransom ?
SQL: select t1.document_object_id from document_subset_members as t1 join document_objects as t2 on t1.document_object_id  =  t2.document_object_id where t2.owner  =  'ransom'

Question: List document that have more than one child. List the document id.
SQL: SELECT T2.Document_Object_ID FROM Document_Objects AS T1 JOIN Document_Objects AS T2 ON T1.Parent_Document_Object_ID = T2.Document_Object_ID GROUP BY T2.Document_Object_ID HAVING count(*)  >  1;

Question: List all collections' subset. List the subsets' names.
SQL: SELECT Collection_Subset_Name FROM Collection_Subsets;

Question: What is detail of collection subset with name 'Top collection'?
SQL: SELECT Collecrtion_Subset_Details FROM Collection_Subsets WHERE Collection_Subset_Name = "Top collection";

Question: For each document object id, how many collections does it belong to?
SQL: SELECT count(*) ,  T2.Document_Object_ID FROM Collections AS T1 JOIN Documents_in_Collections AS T2 ON T1.Collection_ID = T2.Collection_ID GROUP BY T2.Document_Object_ID

Question: List subset id, name and number of different documents in each subset.
SQL: SELECT T1.Document_Subset_ID ,  T2.Document_Subset_Name , count(DISTINCT T1.Document_Object_ID) FROM Document_Subset_Members AS T1 JOIN Document_Subsets AS T2 ON T1.Document_Subset_ID =  T2.Document_Subset_ID GROUP BY T1.Document_Subset_ID;

Question: What are the different descriptions of all the parent documents?
SQL: SELECT DISTINCT T2.Description FROM Document_Objects AS T1 JOIN Document_Objects AS T2 ON T1.Parent_Document_Object_ID = T2.Document_Object_ID

Question: What is the unique description of every parent document?
SQL: SELECT DISTINCT T2.Description FROM Document_Objects AS T1 JOIN Document_Objects AS T2 ON T1.Parent_Document_Object_ID = T2.Document_Object_ID

Question: How many collections that are related to collection named Best?
SQL: SELECT count(DISTINCT T1.Related_Collection_ID) FROM Collection_Subset_Members AS T1 JOIN Collections AS T2 ON T1.Collection_ID  =  T2.Collection_ID WHERE T2.Collection_Name = "Best";

Question: Which document has between 2 and 4 number of documents ? List the document id and the number of related documents .
SQL: select document_object_id , count(*) from document_subset_members group by document_object_id having count(*) between 2 and 4;