<div class="codebody" id="code62597"> --执行顺序 From Where Select select from (select sal as salary,comm as commission from emp ) x where salary<5000 --得出 Name Work as a Job select ename +' Work as a'+job as msg from emp where deptno=10 --如果员工工资小于2000返回UnderPaid 大于等于4k 返回OverPaid 之间返回OK select ename,sal, case when sal<2000 then 'UnderPaid' when sal>=4000 then 'OverPaid' else 'OK' end from emp --从表中随机返回N条记录 newid() --order by 字句中指定数字常量时，是要求根据select列表中相应位置的列排序 --order by 字句中用函数时，则按函数在没一行计算结果排序 select top 5 ename from emp order by newid() --找空值is null select from emp where comm is null --将空值转换为实际值 --解释：返回其参数中第一个非空表达式 --coalesce 联合，合并，结合.英音：[,kəuə'les]美音：[,koə'lɛs] select coalesce(comm,1),empNo from emp --按模式搜索 --返回匹配特定子串或模式的行 select ename,job from emp where deptno in(10,20) --按子串排序 按照职位字段的 最后两个字符排序 select ename,job from emp order by substring(job,len(job)-2,2) --select top 2 len(job)-2 from emp --select top 2 job from emp --☆☆☆☆☆处理排序空值☆☆☆☆☆ [只能是大于0] select ename,comm from emp order by 1 desc -- 以降序或升序方式排序非空值，将空值放到最后，可以用case select ename,comm from ( select ename,comm, case when comm is null then 0 else 1 end as A from emp ) x order by A desc,comm desc
