01-jdbc回顾

database

create database web08 character set gbk;

show create database web08;

select database();  -- 查看正在使用的数据库

use web08;   -- 没有 'database'

table

create table user (
uid int(32) primary key auto_increment,
uname varchar(32),
upwd varchar(32)
)    -- mysql中是varchar, oracle中是varchar2

show tables;   -- 显示所有表

desc user;  -- 建表细节

drop table user；
--------------------------------------

alter table user add uage int(32) not null;   -- 增加一列
...              modify 列名 类型(长度) 约束;   -- 修改某列长度或约束
...              change 旧列名 新列名 类型(长度) 约束;  -- 修改整列
...              drop 列名
rename table 表名 to 新表名;     -- 改表名
alter table 表名 character set 字符集;    -- 修改字符集

set names gbk;   -- 解决姓名中文乱码  ？？

DML

自动增长的列插入时可以用null占位

外键 一对多(主对从)，多(从表)的一侧建外键

create table category (              -- 商品目录表
cid varchar(32) primary key,
cname varchar(100)
);

create table product(                -- 商品表
pid varchar(32) primary key,
pname varchar(40),
price double,
category_id varchar(32)
);

alter table product add foreign key(category_id) references category(cid);  -- 没有constraint
-- 此时可以删除从表的数据，但是主表就不能删除了，若主表删除了一行，则少了一列主键，则违反从表中外键约束
' a foreign key constraint fails '

alter table product drop foreign key 外键名称(一般以 '_fk' 结尾)

多对多的情况 学生选课 — 制造一张中间表，包含两张表的主键分别作为外键

alter table 学生_课程表 add foreign key(学号) references 学生表(学生id);
alter table 学生_课程表 add foreign key(课程号) reference 课程表(课程id);

订单多对多表
create table orderitem(
oid varchar(50),
pid varchar(50)
);

alter table orderitem add CONSTRAINT orderitem_fk FOREIGN key(oid) references orders(oid);
alter table orderitem add CONSTRAINT orderitem_product_fk foreign key(pid) references product(pid);   --  有constraint

多表查询

交叉连连

select * from category,product

内连接 inner join

前提：
alter table product add foreign key(category_id) references category(cid);  -- 没有constraint
显式：select * from category inner join product on cid=category_id
隐式：select * from category c, product p where c.cid=p.category_id

外连接 outer join (outer可省略) —左外连接、右外连接

显式：
select * from category left join product on cid=category_id (结果同上)
select * from category right join product on cid=category_id(结果同上)

insert into category values('c004', null);
insert into product values('p010', 'iphone', 900, null)

select * from<
be25
/span> category left join product on cid=category_id

select * from category right join product on cid=category_id

隐式：
连null那条记录都不显示，只显示有值的交集记录

子查询

查询化妆品类别下的商品
select * from product where category_id = (select cid from category where cid = 'c003')

下面的jdbc不想记了，做项目时不是这样写的，小项目现用DBUtils

DBUtils

QueryRunner(Datasource ds)
ResultSetHandler

QueryRunner

update(String sql, Object... params)
query(String sql, ResultSetHandler<T> rsh, Object... params)

ResultSetHandler

CRUD

public void testAddUser() {
//1. 创建QueryRunner
QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
//2. 写sql
String sql = "insert into user values(null, ?, ?)";
//3. 所有参数都放到参数数组中
Object[] params = {"caocao", "haha"};

try {
int rows = qr.update(sql, params);
if(rows > 0) {
System.out.println("success.");
} else {
System.out.println("failed");
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}    //增删改都差不多

@Test
public void testQueryAll() {
QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());

String sql = "select * from user";

try {
List<User> list = qr.query(sql, new BeanListHandler<User>(User.class));
for (User user : list) {
System.out.println(user);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

@Test
public void testQueryBy() {
QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());

String sql = "select * from user where uname = ?";
Object[] params = {"liubei"};

try {
User user = qr.query(sql, new BeanHandler<User>(User.class), params);
System.out.println(user);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

//查询个数 count(*)
QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());

String sql = "select count(*) from user";

try {
Long count = (Long) qr.query(sql, new ScalarHandler());
System.out.println(count);
...

完结撒花