SQL查询从多值列中提取数据，但前提是它满足特定条件

Question

I have a table doc_source which contains id, document_id and file_name.
The file_name contains various file types such as *pdf, *dgn, *doc, etc. I need to write a query which will pull all documents that have *pdf files and only *pdf files. In other words, lets say I have the following data:

ID  DOCUMENT_Id FILE_NAME
1   100     abc.pdf
2   100     def.doc
3   200     ghi.pdf
4   300     jkl.pdf
5   300     mno.doc

I want to pull all the documents that have only pdfs. So in this case, I'd want a query that extracts only Doc Id 200 since that is the only one which has ONLY pdfs and no other file types.

I tried doing something like this, but something is obviously not quite right:

WITH T1 AS (SELECT DOCUMENT_ID, FILE_NAME FROM DOC_SOURCE)
SELECT DOCUMENT_ID, FILE_NAME FROM DOC_SOURCE AS T2
WHERE FILE_NAME LIKE '%PDF'
GROUP BY DOCUMENT_ID, FILE_NAME
HAVING COUNT(DOCUMENT_ID) = (SELECT COUNT(DOCUMENT_ID) FROM T1)

Answer 1

I would use group by and having :

select document
from t
group by document
having sum(case when file_name like '%.pdf' then 1 else 0 end) = count(*);

That is, the number of file names for each document that end in pdf is equal to the total number of documents.