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select * from emp,dep;
select * from emp,dep where emp.dep_id = dep.id;
select * from emp,dep where emp.dep_id = dep.id and dep.name = "技术";select * from emp inner join dep on emp.dep_id = dep.id;
select * from emp inner join dep on emp.dep_id = dep.id
where dep.name = "技术";
inner join 连接两个表, where过滤条件,只取条件符合的select * from emp left join dep on emp.dep_id = dep.id;select * from emp right join dep on emp.dep_id = dep.id;select * from emp left join dep on emp.dep_id = dep.id
union
select * from emp right join dep on emp.dep_id = dep.id;
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