SqlServer 基础知识-数据检索、查询排序

--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

 

---------------------------------------------2011-11-02 常见 基本的 分页SQL 语句---------------------------------------------------------

壹：

SELECT TOP 页大小 *

FROM table 

WHERE id NOTIN

           (

          SELECT TOP 页大小*(页数-1) id FROM table  ORDERBY id

           )

ORDERBY id

贰：

SELECT TOP 页大小 *

FROM table 

WHERE id >

           (

          SELECTISNULL(MAX(id),0) 

           FROM 

                 (

                 SELECT TOP 页大小*(页数-1) id FROM table  ORDERBY id

                 ) A

           )

ORDERBY id

叁：

SELECT TOP 页大小 * 

FROM 

         (

        SELECT ROW_NUMBER() OVER (ORDERBY id) AS RowNumber *FROM table 

         ) A

WHERE RowNumber > 页大小*(页数-1) 
若查询所有：SELECT  * , ROW_NUMBER() OVER (ORDERBY id) AS RowNumber *FROM table