sql 单表查询练习

-- 工资高于3000的员工
select * from emp where sal > 3000;
-- 工资在2500和3000之间的员工
select * from emp where sal <= 3000 and sal >= 2500;
-- 指定日期后入职的员工
select * from emp where hiredate > '1982-1-1';
-- 查找首字母是S的员工
select * from emp where ename like 'S%';
-- 查找第三个字母是O的员工
select * from emp where ename like '__O%';
-- in 关键字
select * from emp where empno in(7788, 7566);
-- 查找没有上级的员工
select * from emp where mgr is null;
-- 查找工资大于500 或是岗位为 manager 的员工，同时首字母必须是大写的J
select * from emp where (sal >= 500 or job = 'MANAGE') AND ename like 'J%';
-- 工资升序
select * from emp order by sal asc; -- 默认
select * from emp order by sal desc;
-- 部门号升序，工资降序
select * from emp order by deptno, sal desc;
-- 年薪降序
select ename, (nvl(sal, 0)+ nvl(comm, 0))*12 "年薪" from emp order by "年薪" desc; -- oracle
select ename, (ifnull(sal, 0)+ ifnull(comm, 0))*12 as yearly_salary from emp order by yearly_salary desc; -- mysql，mysql 不可以使用中文别名排序
-- 工资最高和最低的员工
select * from emp where sal=(select max(sal) from emp) or sal=(select min(sal) from emp);
-- 所有员工的平均工资和工资总和以及最高工资
select avg(sal) 平均工资, sum(sal) 工资总和, max(sal) 最高工资 from emp;
-- 工资高于平均工资的员工
select * from emp where sal >= (select avg(sal) from emp);
-- 显示每个部门的平均工资和最高工资
select deptno, avg(sal), max(sal) from emp group by deptno;
-- 显示每个部门每个岗位的平均工资和最高工资
select deptno, job, avg(sal), max(sal) from emp group by deptno, job order by deptno;
-- 显示平均工资低于2000的部门的编号和平均工资
select deptno, avg(sal) from emp group by deptno having avg(sal) < 2000 order by avg(sal);
-- 分组函数只能出现在选择列、having及order by 子句中