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码字定式之SQL(2)

select 基本构成之经典格式
  1. select * from emp;
  2. select * from emp where empno>8000;
  3. select empno,ename,sal,comm from emp where sal<comm;
  4. select deptno,count(*) from emp group by deptno;
  5. select deptno,sum(sal) total_sal from emp where job=‘MANAGER‘ group by deptno;
  6. select job,count(distinct deptno) from emp where mgr is not null group by job order by job;
  1. select job,count(distinct deptno) from emp where mgr is not null group by job order by count(distinct deptno) desc,job;
  2. select job, count(distinct deptno) uniq_deptno from emp where mgr is not null group by job order by uniq_deptno desc, job;
  3. select deptno, to_char(hiredate,‘yyyy‘),count(*) from emp group by deptno,to_char(hiredate,‘yyyy‘);
排序是很耗资源的,所以是最后执行,大家应该记住这一点。
下面看一则需求。





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码字定式之SQL(2)