mysql數據庫---sql語句的練習

sql語句的相關總結

練習一：

//創建種類表：
create table category(
cid int primary key auto_increment,
cname varchar(10),
cdesc varchar(31)
);
insert into category values(null,'手機數碼','電子產品'),
(null,'鞋靴箱包','江南皮革廠'),
(null,'香菸酒水','二鍋頭'),
(null,'酸奶','哇哈哈'),
(null,'小零食','辣條');

//創建商品表：
create table product(
pid int primary key auto_increment,
pname varchar(10),
price double,
pdate timestamp.
cno int
);
insert into product values
(null,'小米',998,null,1),
(null,'錘子',2888,null,1),
(null,'阿迪王',99,null,2),
(null,'老村長',88,null,3),
(null,'勁酒',35,null,3),
(null,'小熊餅乾',1,null,4),
(null,'衛龍辣條',1,null,5),
(null,'旺旺大餅',1,null,5);

查詢：
select …
from…
是先執行from在執行select

表別名：

select p.pname,p.price from product as p;

列別名：

select pname as 商品名稱,price as 商品價格 from product ;

查詢所有價格:

select price from product;

去重：

select distinct price from product;

select運算查詢:僅僅在查詢結果上做運算

select *,price*1.5 as 折後價 from product;

條件查詢 where關鍵字

select * from product where price > 60;

<> : 不等於，標準sql語句
!= : 不等於，非標準sql語句

select * from product where price <> 88;

查詢價格10到100的：

select * from product where price > 10 and price <100;

between…and…

select * from product where price between 10 and 100;

邏輯運算 and or not

–like ：模糊查詢
_ :代表的是一個字符
% :代表的是多個字符

查詢出名字帶有餅的所有商品

select * from product where pname like '%餅%';

查詢第二個名字是熊的所有商品

select * from product where pname like '_熊%';

in在某個範圍中獲得值
查詢出商品分類ID在1，4，5裏面的所有商品

select * from product where cno in (1,4,5);

排序查詢： order by 關鍵字
asc: ascend 升序(默認)
desc: descend 降序
1,查詢所有商品，按照價格排序

select * from product order by price ;
select * from product order by price desc;

2,查詢名稱中包含 小的商品，按照價格升序排序

select * from product where pname like '%小%' order by price asc;

–聚合函數：
sum() : 求和
avg() : 求平均值
count() : 統計數量
max() : 最大值
min() : 最小值

1，獲取商品價格的總和

select sum(price) from product;

2，獲取商品價格的平均值

select avg(price) from product;

3，獲取所有商品的個數

select count(*) from product;

注意：where 條件後面不能接聚合函數
4，查出商品價格大於平均價格的所有商品

select * from product where price >(select avg(price) from product);

分組：group by
1,根據cno字段分組，分組後統計商品的個數

select cno,count(*) from product group by cno;

2,根據cno分組，分組統計每組商品的平均價格，並且商品平均價格>60

select cno,avg(price)  from product group by cno having avg(price)>60;	

having 關鍵字 可以接聚合函數的 出現在分組之後
where 關鍵字 不可以聚合函數 出現在分組之前

–編寫順序
– S…F…W…G…H…O

–執行順序

F..W..G..H..S..O

from.. where.. group by.. having.. select.. order by

練習二：

員工信息表

CREATE TABLE emp(
	empno INT,
	ename VARCHAR(50),
	job VARCHAR(50),
	mgr	INT,
	hiredate DATE,
	sal	DECIMAL(7,2),
	comm DECIMAL(7,2),
	deptno INT
) ;

INSERT INTO emp values(7369,'SMITH','CLERK',7902,'1980-12-17',800,NULL,20);
INSERT INTO emp values(7499,'ALLEN','SALESMAN',7698,'1981-02-20',1600,300,30);
INSERT INTO emp values(7521,'WARD','SALESMAN',7698,'1981-02-22',1250,500,30);
INSERT INTO emp values(7566,'JONES','MANAGER',7839,'1981-04-02',2975,NULL,20);
INSERT INTO emp values(7654,'MARTIN','SALESMAN',7698,'1981-09-28',1250,1400,30);
INSERT INTO emp values(7698,'BLAKE','MANAGER',7839,'1981-05-01',2850,NULL,30);
INSERT INTO emp values(7782,'CLARK','MANAGER',7839,'1981-06-09',2450,NULL,10);
INSERT INTO emp values(7788,'SCOTT','ANALYST',7566,'1987-04-19',3000,NULL,20);
INSERT INTO emp values(7839,'KING','PRESIDENT',NULL,'1981-11-17',5000,NULL,10);
INSERT INTO emp values(7844,'TURNER','SALESMAN',7698,'1981-09-08',1500,0,30);
INSERT INTO emp values(7876,'ADAMS','CLERK',7788,'1987-05-23',1100,NULL,20);
INSERT INTO emp values(7900,'JAMES','CLERK',7698,'1981-12-03',950,NULL,30);
INSERT INTO emp values(7902,'FORD','ANALYST',7566,'1981-12-03',3000,NULL,20);
INSERT INTO emp values(7934,'MILLER','CLERK',7782,'1982-01-23',1300,NULL,10);
INSERT INTO emp values(7981,'MILLER','CLERK',7788,'1992-01-23',2600,500,20);

部門信息表

CREATE TABLE dept(
	deptno		INT,
	dname		varchar(14),
	loc		varchar(13)
);

INSERT INTO dept values(10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO dept values(20, 'RESEARCH', 'DALLAS');
INSERT INTO dept values(30, 'SALES', 'CHICAGO');
INSERT INTO dept values(40, 'OPERATIONS', 'BOSTON');

基本查詢

--所有員工的信息
select e.*,d.dname,d.loc from emp e inner join dept d on d.deptno = e.deptno;

--薪資大於等於1000並且小於等於2000的員工信息
select e.*,d.dname,d.loc from emp e inner join dept d on d.deptno = e.deptno and e.sal>=1000 
and e.sal<=2000;

--從員工表中查詢出所有的部門編號
select distinct e.deptno from emp e;

--查詢出名字以A開頭的員工的信息
select e.*,d.dname,d.loc from emp e inner join dept d on d.deptno = e.deptno and e.ename like 'A%';

--查詢出名字第二個字母是L的員工信息
select * from emp where ename like '_L%';

--查詢出沒有獎金的員工信息
select * from emp where comm is null;

--所有員工的平均工資
select avg(sal) as 平均工資 from emp;

--所有員工的工資總和
select sum(sal) as 總和 from emp;

--所有員工的數量
select count(*) from emp;

--最高工資
select max(sal) from emp;

--最少工資
select min(sal) from emp;

--最高工資的員工信息
select * from emp where sal = (select max(sal) from emp)

--最低工資的員工信息
select * from emp where sal = (select min(sal) from emp)

分組查詢

--每個部門的平均工資
select deptno,avg(sal) as 平均工資 from emp group by deptno;

子查詢

-- 單行子查詢(> < >= <= = <>)
	-- 查詢出高於10號部門的平均工資的員工信息
	select * from emp where sal >(select avg(sal) from emp where  deptno=10);
	
-- 多行子查詢(in  not in any all)    >any  >all
	-- 查詢出比10號部門任何員工薪資高的員工信息
	select * from emp where sal >(select max(sal) from emp where  deptno=10);
	
-- 多列子查詢(實際使用較少)   in
	-- 和10號部門同名同工作的員工信息	
select * from emp where deptno<>10 and (ename,job) in (select ename,job from emp where deptno=10)
		
-- Select接子查詢
	-- 獲取員工的名字和部門的名字
	select e.ename , d.dname from emp e,dept d where e.deptno = d.deptno
	
-- from後面接子查詢
	-- 查詢emp表中經理信息
	select * from emp where job='MANAGER';
	
-- where 接子查詢
	-- 薪資高於10號部門平均工資的所有員工信息
	select * from emp where sal>(select avg(sal) from emp where deptno=10)
	
-- having後面接子查詢
	-- 有哪些部門的平均工資高於30號部門的平均工資	
	select deptno, avg(sal) from emp group by deptno having avg(sal)
	 >(select avg(sal) from emp where deptno=30)
	
-- 工資>JONES工資
select * from emp where sal >(select sal from emp where ename='JONES')

-- 查詢與SCOTT同一個部門的員工
select * from emp where deptno = (select deptno from emp where ename='SCOTT')

-- 工資高於30號部門所有人的員工信息
select * from emp where sal >(select max(sal) from emp where deptno =30)

SQL查詢的綜合案例

--查詢出高於本部門平均工資的員工信息
select * from emp e where sal > (select avg(sal) from emp where e.deptno = deptno)

--列出達拉斯加工作的人中,比紐約平均工資高的人
select * from emp where deptno =(select deptno from dept where loc='DALLAS') 
and sal>(select avg(sal) from emp where deptno=(select deptno from dept where loc='NEW YORK'))

--查詢出各個部門薪水最高的員工所有信息
select * from emp e where sal =(select max(sal) from emp where deptno=e.deptno)