获取没有文档的文件夹

I use this query to get the number of documents the folder contains:

$query = " 
        SELECT
            *,
            count(*) as number_documents
        FROM
            table_documents
        LEFT JOIN
            table_folders ON folder_id = document_folder_id
        GROUP BY
            document_folder_id
        ORDER BY
            number_documents DESC
";

I can't get the folders with 0 documents, how do i get the folders to have:

FOLDER 1 - 100 documents

FOLDER 2 - 35 documents

FOLDER 3 - 0 documents

TABLES:

**table_folders**
folder_id
folder_description
folder_active

**table_documents**
document_id
document_folder_id
document_description
document_file

I think you have to sum the documents from the document folder. Try the query

SELECT d.document_folder_id
     , SUM(d.documents) as number_documents 
  FROM table_documents d 
  LEFT 
  JOIN table_folder f 
    ON f.folder_id = d.document_folder_id 
 GROUP BY d.document_folder_id 

since you dint clearly explained about the table structure .I have created table locally and tried , Try the query which i have tried locally

create table table_documents(id int,doc int);
insert into table_documents values
(1,100),
(2,35),
(3,0),
(1,101),
(2,36),
(3,0);

create table table_folder(id int);
insert into table_folder values
(1),(2),(3);

SELECT d.id
     , SUM(d.doc) as number_documents 
  FROM table_documents d 
  LEFT 
  JOIN table_folder f 
    ON f.id = d.id 
 GROUP 
    BY d.id;// query for your output 

This will work:

        SELECT
            *,
            sum(if (document_folder_id is null,0,1)) as number_documents
        FROM
            table_folders
        LEFT JOIN
            table_documents ON document_folder_id = folder_id
        GROUP BY
            folder_id
        ORDER BY
            number_documents DESC