sql server查询(SELECT ,where,distinct,like 查询,in,is null,group by 和having,order by,as)

基本查询:

实例表

 1 示例表
 2 --部门表
 3 
 4 create table dept(
 5 
 6    deptno int primary key,--部门编号
 7 
 8    dname nvarchar(30),--部门名
 9 
10    loc nvarchar(30)--地址
11 
12 );
13 
14  
15 
16 --雇员表
17 
18 create table emp(
19 
20    empno int primary key,--雇员号
21 
22    ename nvarchar(30),--员工姓名
23 
24    job   nvarchar(30),--雇员工作
25 
26    mrg int,--雇员上级
27 
28    hiredate datetime,--入职时间
29 
30    sal numeric(10,2),--薪水
31 
32    comm numeric(10,2),--奖金
33 
34    deptno int foreign key references dept(deptno)--设置外键
35 
36 );
37 
38  
39 
40 insert into dept values (10,"ACCOUNTING","NEW YORK");
41 
42 insert into dept values (20,"RESEARCH","DALLAS");
43 
44 insert into dept values (30 ,"SALES","CHICAGO");
45 
46 insert into dept values (40, "OPERATIONS","BOSTON");
47 
48  
49 
50 insert into emp values (7369,"SMITH","CLERK",7902,"1980-12-17",800.00,null,20);
51 
52 insert into emp values(7499,"ALLEN","SALESMAN",7698,"1981-2-20",1600.00,300.00,30);
53 
54 insert into emp values(7521,"WARD","SALESMAN",7698,"1981-2-22",1250.00,500.00,30);
55 
56 insert into emp values(7566,"JONES","MANAGER",7839,"1981-4-2",2975.00,null,20);
57 
58 insert into emp values(7654,"MARTIN","SALESMAN",7698,"1981-9-28",1250.00,1400.00,30);
59 
60 insert into emp values(7698,"BLAKE","MANAGER",7839,"1981-5-1",2850.00,null,30);
61 
62 insert into emp values(7782,"CLARK","MANAGER",7839,"1981-6-9",2450.00,null,10);
63 
64 insert into emp values(7788,"SCOTT","ANALYST",7566,"1987-4-19",3000.00,null,20);
65 
66 insert into emp values(7839,"KING","PRESIDENT",null,"1981-11-17",5000.00,null,10);
67 
68 insert into emp values(7844,"TURNER","SALESMAN",7698,"1981-9-8",1500.00,0.00,30);
69 
70 insert into emp values(7876,"ADAMS","CLERK",7788,"1987-5-23",1100.00,null,20);
71 
72 insert into emp values(7900,"JAMES","CLERK",7698,"1981-12-3",950.00,null,30);
73 
74 insert into emp values(7902,"FORD","ANALYST",7566,"1981-12-3",3000.00,null,20);
75 
76 insert into emp values(7934,"MILLER","CLERK",7782,"1982-1-23",1300.00,null,10);
View Code
 1 select
 2 基本select语句
 3 
 4 select [distinct] *|{列名1, 列名2,列名3...} 
 5 
 6 from  表名 [where (条件)];
 7 
 8  
 9 
10 说明:
11 
12 select 指定查询哪些列的数据。
13 
14 *号代表查询所有列。
15 
16 from指定查询哪张表。
17 
18 where 表示条件。
19 
20 distinct可选,指显示结果时,是否剔除重复数据
21 
22  
23 
24 简单的查询语句
25 
26  
27 
28 ■ 查询所有列
29 
30 select * from 表名;
31 
32 ■ 查询指定列
33 
34 select 列1,列2… from 表名;
35 
36 select ename,sal from emp;
37 
38 ■ 如何取消重复行
39 
40 select distinct deptno ,job from emp;
41 
42 ?查询SMITH 的薪水,工作,所在部门
43 
44 select sal,job,deptno from emp where ename="SMITH";
45 
46 特别说明:SQLServer 的sql 不区分大小写,内容也不区分大小写
47 
48  
49 
50 ■ 使用算数表达式
51 
52 ?显示每个雇员的年工资(奖金为null的用0代替)
53 
54 select ename,sal*12+isnull(comm,0)*12 as "年薪" from emp;
55 
56 说明:isnull函数是 SQLserver提供的,用于处理数据 null 的问题
57 
58  
59 
60 ■ 使用列的别名
61 
62 select ename "姓名",sal*12 as "年收入" from emp;
63 
64  
65 
66 使用别名时,as 可省略,别名可用单引号,双引号或者不加
67 
68  
69 
70 查询工资在 20005000 的员工情况
71 
72 ①,     select * from emp where sal>=2000 and sal<=3000;
73 
74 ②,     select * from emp where sal between 2000 and 3000;

where

使用where子句

如何显示工资高于的员工

select ename from emp where sal>3000;

 

如何显示工资在到的员工情况

select * from emp where sal>=2000 and sal<=250;

 

select * from emp where sal between 2000 and 2500;(闭区间)

distinct

distinct可选,指显示结果时,是否剔除重复数据

 

select [distinct] * from emp;

like 查询

%: 表示任意0到多个字符 

_: 表示任意单个字符

不区分大小写

如何显示首字符为S的员工姓名和工资

select ename,sal from emp where ename like "S%";

 

如何显示第三个字符为O的所有员工的姓名和工资

select ename,sal from emp where ename like "__O%";

 

查询首字母不是 S 的雇员信息

select ename,job from emp where ename not like "S%";

in

如何显示empno为123,345,800...的雇员情况

 

①,select * from emp where empno=123 or empno=345 or empno=800;

 

②,select * from emp where empno in (123,456,800);

一般我们使用 in 这个关键字,这样效率更高

is null

如何显示没有上级的雇员的情况

select * from emp where mgr is null;

 

group by 和having(重点)

 1 group by用于对查询的结果分组统计,默认升序
 2 
 3 having子句用于限制分组显示结果.
 4 
 5  
 6 
 7 使用order by字句
 8 
 9 如何按照工资的从低到高的顺序显示雇员的信息
10 
11 select ename,sal from emp order by sal asc;
12 
13 按照部门号升序而雇员的工资降序排列
14 
15 select * from emp order by deptno asc,sal desc;
16 
17 按照入职先后顺序排序
18 
19 select ename,hiredate from emp order by hiredate asc;
20 
21 ■使用列的别名排序
22 
23 select ename,sal*12 "年薪" from emp order by "年薪" asc;
24 
25 别名需要使用""号圈中,也可以不在""号圈中。
26 
27  
28 
29 如何显示每个部门的平均工资和最高工资
30 
31 select avg(sal),max(sal),deptno from emp group by deptno;
32 
33  
34 
35 显示每个部门的每种岗位的平均工资和最低工资
36 
37 select avg(sal),max(sal),deptno,job from emp group by deptno,job order by deptno;
38 
39  
40 
41 显示部门平均工资低于2000的部门号和它的平均工资
42 
43 思路:   
44 
45 1,查询出各个部门的平均工资
46 
47 select avg(sal),deptno from emp group by deptno;
48 
49  
50 
51 2,挑选出低于的
52 
53 select avg(sal),deptno from emp group by deptno having avg(sal)<2000;
54 
55  
56 
57  
58 
59 对数据分组的总结
60 
61 1  分组函数只能出现在选择列表、havingorder by子句种
62 
63 2 如果在select 语句种同时包含有group by ,having ,
64 
65 order by 那么他们的顺序是group by , having , order by
66 
67 3 在选择列中,如果有列、表达式、和分组函数,那么这些列和
68 
69 表达式必须有一个出现在group by 子句中,否则就会出错
70 
71 select deptno,avg(sal),max(sal) from emp group by deptno having avg(sal)<2000;
72 
73 这里deptno就一定要出现在 group by

order by

 1 order by 子句用于排序结果集。
 2 
 3 asc表示升序
 4 
 5 desc表示降序
 6 
 7  
 8 
 9 如何按照工资的从低到高的顺序显示雇员的信息
10 
11 select * from emp order by sal [asc];
12 
13  
14 
15 查询学生信息,按照学号升序排列
16 
17 select * from student order by sno;
18 
19 查询学生信息,按照年龄降序排列
20 
21 select * from student order by sage desc;
22 
23 查询学生信息,按照年龄降序排列,如果年龄相等再按照学号升序排列
24 
25 select * from student order by sage desc,sno asc;

使用别名

 1 1)   select ename,sal "薪水" from emp;
 2 
 3 2)   select ename,sal "薪水" from emp;
 4 
 5 3)   select ename,sal 薪水from emp;
 6 
 7 4)   select ename,sal as "薪水" from emp;
 8 
 9 5)   select ename,sal as "薪水" from emp;
10 
11 6)   select ename,sal as 薪水from emp;
12 
13  
14 
15 ■使用列的别名排序
16 
17 select ename,sal*12 "年薪" from emp order by "年薪" asc;