数据库两张表格关联使用案例

查询课程编号(cno)是1002的,学员的编号(sno),姓名(sname),年龄(age),地址(address)

• select sno,sname,age,address from stu01 where sno in( select sno from sco01 where cno=1002);   ----使用嵌套查询
• select a.sno, sname,age,address from stu01 as a,sco01 as b where a.sno=b.sno and cno=1002;

语法格式：select * from 表1,表2 where 表1.name=表2.name;  → 本题中要查询的是stu01表中的sno, sname,age,address，将stu01命别名为a，sco01别名b，stu01 as a,sco01对应语句中的表1表2，a.sno=b.sno and cno=1002对应语句中的表1.name=表2.name;

• select a.sno, sname,age,address from stu01 a left join sco01 b on a.sno=b.sno where b. cno=1002;

------left join....on...向左链接