目錄

零、碼仙勵志

不被嘲笑的夢想是沒有價值的。願你的夢想不只是空談的情懷，而是實幹的姿態

一、建庫和建表

create database scort
use scort
create table emp
(
	empno int primary key,
	ename nvarchar(10),
	sal int,
	deptno int
)
insert into emp values (7369,'smith',3000,20);
insert into emp values (7499,'allen',1500,10);
insert into emp values (7521,'ward',2850,30);
insert into emp values (7566,'jones',2000,30);
insert into emp values (7654,'martin',5000,10);
insert into emp values (7698,'blake',1800,30);

create table dept
(
	deptno int primary key,
	dname nvarchar(10),
	loc nvarchar(10)
)
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');

create table salgrade
(
	grade int primary key,
	lostl int,
	hisal int
)
insert into salgrade values (1,700,1200);
insert into salgrade values (2,1201,1400);
insert into salgrade values (3,1401,2000);
insert into salgrade values (4,2001,3000);
insert into salgrade values (5,3001,6000);
 

二、內連線的用法(inner join)

解釋：將兩個表或兩個以上的表以一定的連線條件連線起來，從中檢索出滿足條件的資料。

注意：inner join 可以簡寫為 join

1.select ...... from A,B 的用法

1.產生的結果：行數是A和B的乘積，列數是A和B之和。或者說把A表的每一條記錄和B表的每一條記錄組合在一起，形成的是個笛卡爾積。

2.select ...... from A,B和select ...... from B,A的輸出查詢結果本質上是一樣的，只是看起來A，B表的前後順序不一樣而已。

3.例項演示：

select * from emp,dept
 

select * from dept,emp

2.select ...... from A,B  where ......的用法(sql92標準)

1.select ...... from A,B  where ......和select ...... fromB,A  where ......查詢結果本質上一樣

select * from emp,dept where sal>2000

2.如果倆個表或多個表有相同列名的時候，where後面必須加表名。

select * from emp,dept where deptno=10 --error

select * from emp,dept where emp.deptno=10
 

select * from emp,dept where dept.deptno=10

3.三張表連線在一起

--把工資大於2000的ename，dname和grade輸出
select "E".ename,"D".dname,"S".grade
	from emp "E",dept "D",salgrade "S"
	where "E".deptno="D".deptno and
		  ("E".sal>"S".lostl and "E".sal<"S".hisal) and
		  "E".sal>2000

3.select ...... from A join B on ......的用法(sql99標準)

1.select ...... from A join B on ......和select ...... from B join A on ......查詢結果本質上一樣

2.倆張表連線在一起

select * from emp
	join dept
	on 1=1

select * from emp
	join dept
	on emp.deptno=dept.deptno

3.三張表連線在一起

--把工資大於2000的ename，dname和grade輸出
select "E".ename,"D".dname,"S".grade
	from emp "E"
	join dept "D"
	on "E".deptno="D".deptno
	join salgrade "S"
	on "E".sal>"S".lostl and "E".sal<"S".hisal
	where "E".sal>2000