企业官网建设流程全解析

商务网站建设论文总结,百度开户渠道商哪里找,网络优化行业怎么样,南宁百度seo排名优化软件表的连接分为内连和外连第一章#xff1a;内连接内连接实际上就是利用where子句对两种表形成的笛卡儿积进行筛选#xff0c;我们前面学习的查询都是内连接#xff0c;也是在开发过程中使用的最多的连接查询。语法#xff1a;select 字段 from 表1 inner join 表2 on 连接条…表的连接分为内连和外连第一章内连接内连接实际上就是利用where子句对两种表形成的笛卡儿积进行筛选我们前面学习的查询都是内连接也是在开发过程中使用的最多的连接查询。语法select 字段 from 表1 inner join 表2 on 连接条件 and 其他条件备注前面学习的都是内连接案例显示SMITH的名字和部门名称-- 用前面的写法 select ename, dname from EMP, DEPT where EMP.deptnoDEPT.deptno and enameSMITH; -- 用标准的内连接写法 select ename, dname from EMP inner join DEPT on EMP.deptnoDEPT.deptno and enameSMITH;示例2mysql select * from emp, dept where emp.deptnodept.deptno; -------------------------------------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | deptno | dname | loc | -------------------------------------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 30 | SALES | CHICAGO | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 30 | SALES | CHICAGO | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | 30 | SALES | CHICAGO | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | 30 | SALES | CHICAGO | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | 30 | SALES | CHICAGO | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | 30 | SALES | CHICAGO | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | -------------------------------------------------------------------------------------------------------------- 14 rows in set (0.00 sec) mysql select ename, dname from emp, dept where emp.deptnodept.deptno; -------------------- | ename | dname | -------------------- | SMITH | RESEARCH | | ALLEN | SALES | | WARD | SALES | | JONES | RESEARCH | | MARTIN | SALES | | BLAKE | SALES | | CLARK | ACCOUNTING | | SCOTT | RESEARCH | | KING | ACCOUNTING | | TURNER | SALES | | ADAMS | RESEARCH | | JAMES | SALES | | FORD | RESEARCH | | MILLER | ACCOUNTING | -------------------- 14 rows in set (0.00 sec) mysql select * from emp inner join dept on emp.deptnodept.deptno; -------------------------------------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | deptno | dname | loc | -------------------------------------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | 30 | SALES | CHICAGO | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | 30 | SALES | CHICAGO | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | 30 | SALES | CHICAGO | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | 30 | SALES | CHICAGO | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | 30 | SALES | CHICAGO | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | 30 | SALES | CHICAGO | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | 20 | RESEARCH | DALLAS | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | 10 | ACCOUNTING | NEW YORK | -------------------------------------------------------------------------------------------------------------- 14 rows in set (0.00 sec) mysql select ename, dname from emp inner join dept on emp.deptnodept.deptno; -------------------- | ename | dname | -------------------- | SMITH | RESEARCH | | ALLEN | SALES | | WARD | SALES | | JONES | RESEARCH | | MARTIN | SALES | | BLAKE | SALES | | CLARK | ACCOUNTING | | SCOTT | RESEARCH | | KING | ACCOUNTING | | TURNER | SALES | | ADAMS | RESEARCH | | JAMES | SALES | | FORD | RESEARCH | | MILLER | ACCOUNTING | -------------------- 14 rows in set (0.00 sec) mysql select ename, dname from emp inner join dept on emp.deptnodept.deptno where enameSMITH; ----------------- | ename | dname | ----------------- | SMITH | RESEARCH | ----------------- 1 row in set (0.00 sec) mysql select ename, dname from emp inner join dept on emp.deptnodept.deptno and enameSMITH; ----------------- | ename | dname | ----------------- | SMITH | RESEARCH | ----------------- 1 row in set (0.00 sec)第二章外连接外连接分为左外连接和右外连接左外连接如果联合查询左侧的表完全显示我们就说是左外连接。语法select 字段名 from 表名1 left join 表名2 on 连接条件案例-- 建两张表 create table stu (id int, name varchar(30)); -- 学生表 insert into stu values(1,jack),(2,tom),(3,kity),(4,nono); create table exam (id int, grade int); -- 成绩表 insert into exam values(1, 56),(2,76),(11, 8);查询所有学生的成绩如果这个学生没有成绩也要将学生的个人信息显示出来-- 当左边表和右边表没有匹配时也会显示左边表的数据 select * from stu left join exam on stu.idexam.id;示例2mysql create table stu (id int, name varchar(30)); Query OK, 0 rows affected (0.01 sec) mysql desc stu; ----------------------------------------------- | Field | Type | Null | Key | Default | Extra | ----------------------------------------------- | id | int(11) | YES | | NULL | | | name | varchar(30) | YES | | NULL | | ----------------------------------------------- 2 rows in set (0.01 sec) mysql insert into stu values(1,jack),(2,tom),(3,kity),(4,nono); Query OK, 4 rows affected (0.01 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql select * from stu; ------------ | id | name | ------------ | 1 | jack | | 2 | tom | | 3 | kity | | 4 | nono | ------------ 4 rows in set (0.00 sec) mysql create table exam (id int, grade int); Query OK, 0 rows affected (0.01 sec) mysql insert into exam values(1, 56),(2,76),(11, 8); Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 mysql select * from exam; ------------- | id | grade | ------------- | 1 | 56 | | 2 | 76 | | 11 | 8 | ------------- 3 rows in set (0.00 sec) mysql select * from stu left join exam on stu.idexam.id; ------------------------- | id | name | id | grade | ------------------------- | 1 | jack | 1 | 56 | | 2 | tom | 2 | 76 | | 3 | kity | NULL | NULL | | 4 | nono | NULL | NULL | ------------------------- 4 rows in set (0.00 sec) mysql select * from stu inner join exam on stu.idexam.id; ------------------------- | id | name | id | grade | ------------------------- | 1 | jack | 1 | 56 | | 2 | tom | 2 | 76 | ------------------------- 2 rows in set (0.00 sec)右外连接如果联合查询右侧的表完全显示我们就说是右外连接。语法select 字段 from 表名1 right join 表名2 on 连接条件案例对stu表和exam表联合查询把所有的成绩都显示出来即使这个成绩没有学生与它对应也要显示出来select * from stu right join exam on stu.idexam.id;示例2mysql select * from stu right join exam on stu.idexam.id; ------------------------- | id | name | id | grade | ------------------------- | 1 | jack | 1 | 56 | | 2 | tom | 2 | 76 | | NULL | NULL | 11 | 8 | ------------------------- 3 rows in set (0.00 sec) mysql select * from exam left join stu on stu.idexam.id; ------------------------- | id | grade | id | name | ------------------------- | 1 | 56 | 1 | jack | | 2 | 76 | 2 | tom | | 11 | 8 | NULL | NULL | ------------------------- 3 rows in set (0.00 sec)练习列出部门名称和这些部门的员工信息同时列出没有员工的部门方法一 select d.dname, e.* from dept d left join emp e on d.deptnoe.deptno; 方法二 select d.dname, e.* from emp e right join dept d on d.deptnoe.deptno;mysql select * from emp; -------------------------------------------------------------------------------- | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------- | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | -------------------------------------------------------------------------------- 14 rows in set (0.00 sec) mysql select distinct deptno from emp; -------- | deptno | -------- | 20 | | 30 | | 10 | -------- 3 rows in set (0.00 sec) mysql select * from dept; ------------------------------ | deptno | dname | loc | ------------------------------ | 10 | ACCOUNTING | NEW YORK | | 20 | RESEARCH | DALLAS | | 30 | SALES | CHICAGO | | 40 | OPERATIONS | BOSTON | ------------------------------ 4 rows in set (0.00 sec) mysql select * from dept left join emp on dept.deptnoemp.deptno; -------------------------------------------------------------------------------------------------------------- | deptno | dname | loc | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------------------------------------- | 20 | RESEARCH | DALLAS | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 30 | SALES | CHICAGO | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 30 | SALES | CHICAGO | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 20 | RESEARCH | DALLAS | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 30 | SALES | CHICAGO | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 30 | SALES | CHICAGO | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 10 | ACCOUNTING | NEW YORK | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 20 | RESEARCH | DALLAS | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 10 | ACCOUNTING | NEW YORK | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 30 | SALES | CHICAGO | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 20 | RESEARCH | DALLAS | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 30 | SALES | CHICAGO | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 20 | RESEARCH | DALLAS | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 10 | ACCOUNTING | NEW YORK | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | | 40 | OPERATIONS | BOSTON | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | -------------------------------------------------------------------------------------------------------------- 15 rows in set (0.00 sec) mysql select * from dept left join emp on dept.deptnoemp.deptno order by dept.deptno asc; -------------------------------------------------------------------------------------------------------------- | deptno | dname | loc | empno | ename | job | mgr | hiredate | sal | comm | deptno | -------------------------------------------------------------------------------------------------------------- | 10 | ACCOUNTING | NEW YORK | 007782 | CLARK | MANAGER | 7839 | 1981-06-09 00:00:00 | 2450.00 | NULL | 10 | | 10 | ACCOUNTING | NEW YORK | 007839 | KING | PRESIDENT | NULL | 1981-11-17 00:00:00 | 5000.00 | NULL | 10 | | 10 | ACCOUNTING | NEW YORK | 007934 | MILLER | CLERK | 7782 | 1982-01-23 00:00:00 | 1300.00 | NULL | 10 | | 20 | RESEARCH | DALLAS | 007902 | FORD | ANALYST | 7566 | 1981-12-03 00:00:00 | 3000.00 | NULL | 20 | | 20 | RESEARCH | DALLAS | 007788 | SCOTT | ANALYST | 7566 | 1987-04-19 00:00:00 | 3000.00 | NULL | 20 | | 20 | RESEARCH | DALLAS | 007876 | ADAMS | CLERK | 7788 | 1987-05-23 00:00:00 | 1100.00 | NULL | 20 | | 20 | RESEARCH | DALLAS | 007369 | SMITH | CLERK | 7902 | 1980-12-17 00:00:00 | 800.00 | NULL | 20 | | 20 | RESEARCH | DALLAS | 007566 | JONES | MANAGER | 7839 | 1981-04-02 00:00:00 | 2975.00 | NULL | 20 | | 30 | SALES | CHICAGO | 007844 | TURNER | SALESMAN | 7698 | 1981-09-08 00:00:00 | 1500.00 | 0.00 | 30 | | 30 | SALES | CHICAGO | 007521 | WARD | SALESMAN | 7698 | 1981-02-22 00:00:00 | 1250.00 | 500.00 | 30 | | 30 | SALES | CHICAGO | 007698 | BLAKE | MANAGER | 7839 | 1981-05-01 00:00:00 | 2850.00 | NULL | 30 | | 30 | SALES | CHICAGO | 007900 | JAMES | CLERK | 7698 | 1981-12-03 00:00:00 | 950.00 | NULL | 30 | | 30 | SALES | CHICAGO | 007499 | ALLEN | SALESMAN | 7698 | 1981-02-20 00:00:00 | 1600.00 | 300.00 | 30 | | 30 | SALES | CHICAGO | 007654 | MARTIN | SALESMAN | 7698 | 1981-09-28 00:00:00 | 1250.00 | 1400.00 | 30 | | 40 | OPERATIONS | BOSTON | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | -------------------------------------------------------------------------------------------------------------- 15 rows in set (0.00 sec) mysql select dname, ename, dept.deptno from dept left join emp on dept.deptnoemp.deptno order by dept.deptno asc; ---------------------------- | dname | ename | deptno | ---------------------------- | ACCOUNTING | KING | 10 | | ACCOUNTING | CLARK | 10 | | ACCOUNTING | MILLER | 10 | | RESEARCH | ADAMS | 20 | | RESEARCH | SCOTT | 20 | | RESEARCH | FORD | 20 | | RESEARCH | JONES | 20 | | RESEARCH | SMITH | 20 | | SALES | MARTIN | 30 | | SALES | ALLEN | 30 | | SALES | JAMES | 30 | | SALES | BLAKE | 30 | | SALES | WARD | 30 | | SALES | TURNER | 30 | | OPERATIONS | NULL | 40 | ---------------------------- 15 rows in set (0.00 sec)