Question

我使用此查询来获取文件夹包含的文档数量：

$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
";

我无法获取包含0个文档的文件夹，如何获取文件夹：

FOLDER 1 - 100份文件

FOLDER 2 - 35个文件

文件夹3 - 0文件

TABLES：

**table_folders**
folder_id
folder_description
folder_active

**table_documents**
document_id
document_folder_id
document_description
document_file

Answer 1

我认为您必须从文档文件夹中汇总文档。尝试查询

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

因为你明确解释了表结构。我已经在本地创建了表并尝试过，尝试我在本地尝试过的查询

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

Answer 2

这将有效：

        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

获取没有文档的文件夹

2 个答案: