mysql多表关联count某张表_MySQL使用JOIN COUNT多个表

我尝试使用连接从多个表中选择总数时遇到问题. COUNT的结果不正确.

我有三张桌子：

Customers

id -> Primary/Autoincrement

name

Documents

id -> Primary/Autoincrement

customer_id

Documents_items

id -> Primary/Autoincrement

document_id

我想获得按客户名称分组的文件和文件项目总数.

SELECT cust.name,

COUNT(doc.id),

COUNT(item.id)

FROM customers AS cust

INNER JOIN documents AS doc ON doc.customer_id = cust.id

INNER JOIN documents_items AS item ON item.document_id = doc.id

GROUP BY cust.name

问题是COUNT(doc.id)的结果等于COUNT(item.id)的结果,这是不正确的.

您可以在SQLFiddle中看到错误的演示示例.

输入示例：

INSERT INTO customers VALUES('John')

INSERT INTO documents VALUES(1)

INSERT INTO documents_items VALUES(1), VALUES(1)

预期产量：

Name | Total Docs | Total Items

John 1 2

当前输出：

Name | Total Docs | Total Items

John 2 2