COUNT(*)和LEFT JOIN

Question

这个查询:

SELECT staff.staff_id, COUNT(references_table.staff_id) 
FROM staff 
LEFT JOIN references_table USING (staff_id)

返回:

staff_id    COUNT(references_table.staff_id)
1            2

我怎么能让它返回0,因为staff_ids没有任何引用的计数？

Answer 1

一个GROUP BY条款将成功

SELECT staff.staff_id, COUNT(references_table.staff_id) 
FROM staff 
LEFT JOIN references_table USING (staff_id)
GROUP BY staff.staff_id