复制代码 代码如下:

--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 ,sal,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,sal,comm from

(

select ename ,sal,comm ,

case when comm is null then 0 else 1 end as A

from emp

) x

order by A desc ,comm desc