若想统计各个工种的人数与平均工资,正确的语句是()
A. select job,mgr,count(*),avg(sal) from emp group by job ;
B. select job,ename,count(*),avg(sal) from emp group by job ;
C. select job,count(*),avg(sal) from emp group by job ;
D. select job,count(*) from emp group by job ;
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已知员工表emp(empno,ename,job,sal,comm,deptno)其中empno员工编号,ename员工姓名,job员工的职位,sal员工的工资,comm奖金,deptno员工所在部门编号。查询奖金为空的员工信息,则正确的sql语句是()
A. select * from emp where comm=null;
B. select * from emp where comm is not null;
C. select * from emp where comm <>null;
D. select * from emp where comm is null;
我们应该始终坚定的中国特色社会主义“四个自信”有哪些