基础查询

##(1.2)查询指定列;
select empno,ename,deptno from emp;

##(2)条件查询where
##(2.1)查询性别女，并且 年龄65的学生记录
select * from stu where gender='female' and age='65';

##（2.2）查询学号是S_1001或者名字为lisi的记录
select * from stu where sid ='S_1001' or age='65';

##(2.3)查询学号是S_1001,S_1002,S_1003的记录
写法一：select * from stu where sid = 'S_1001' or sid = 'S_1002' or sid = 'S_1003';
写法二：select * from stu where sid in('S_1001','S_1002','S_1003');

##(2,4) 查询学号不是S_1001,S_1002,S_1003的记录
select * from stu where sid not in('S_1001','S_1002','S_1003');

##(2.5)查询年龄为null的记录
select * from stu where age is null;

##(2.6)查询名字不为空的学习信息
select * from stu where sname is not null;

##(2.7)查询年龄为20-40岁之间的
方法一：select *from stu where age >=20 and age <=40;
方法二：select *from stu where age between 20 and 40;

##(2.6)查询性别：非男的 学生记录
select *from stu where gender !='male';
select *from stu where gender <>'male';
select *from stu where not gender = 'male';