使用SQL計算行

Question

請幫助我創建SQL查詢。

我有兩個表格，公司和用戶。用戶表中有company_id字段。

我需要統計有多少公司根本沒有用戶。

任何幫助都會很好！謝謝！

Answer 1

SELECT COUNT(*) 
FROM companies a LEFT JOIN users b 
     on a.company_ID = b.company_ID 
WHERE b.company_ID IS NULL 

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Answer 2

SELECT COUNT(*) 
FROM companies c 
WHERE NOT EXISTS 
(
    SELECT 1 FROM users u 
    WHERE u.company_id = c.company_id 
) 

Answer 3

SELECT COUNT(*) 
FROM companies c LEFT JOIN users u 
ON c.company_id = u.company_id 
WHERE u.company_id IS NULL 

Answer 4

Select Count(tblCompanies.ID) 
From tblCompanies 
left join tblUsers ON tblCompanies.ID = tblUsers.CompanyID 
Where tblUsersID IS Null 
Group By tblCompanies.ID