SELECT COUNT(companyId)
FROM Companies
LEFT JOIN Cities ON Cities.cityId = Companies.cityId
GROUP BY Companies.companyId;
VS
SELECT COUNT(companyId)
FROM Cities
LEFT JOIN Companies ON Cities.cityId = Companies.cityId
GROUP BY Companies.companyId;
的区别是什么?这两个MySQL查询有什么区别?
你跑过了吗? –
查看左连接中的左端是什么意思,你就会得到你的答案。 – ceejayoz
做作业? – Kawu