摘要：1.连接查询 1.内连接 select * from student st inner join number mu on st.id = nu.type,id; 2.左连接 select * from student st left join number mu on st.id = nu.typ 阅读全文

摘要：2.条件查询: 1.比较运算符:<,>,=,<=,>= selsect * from 表 where num > 30 and grade < 90; 2.逻辑运算符:not,and,or selsect * from 表 where not num = 30 and grade < 90; 注意： 阅读全文