二、數據庫中表的操作
0.mysql數據庫中的數據類型
1.增加表
CREATE TABLE 表名
(
字段名1,數據類型[完整性約束條件],
字段名2,數據類型[完整性約束條件],
......
字段名n,數據類型[完整性約束條件],
)
//創建表之間一定先連接一個數據庫!
~創建一張學生表student
create table student
(
xh char(12),
name char(12),
sex char(5),
age int
);
2.查看錶
查看錶結構:desc 表名;
查詢當前數據庫中的所有表:show tables;
查看錶的建表語句:show create table 表名;
3.修改表(ALTER TABLE語句)
~添加新的字段(列)
alter table book1 add xb char(3)//如果同時添加多個字段ADD後加括號
~修改字段屬性
Alter table +表名 modify xh char(12);
~刪除字段
Alter table +biaoming drop bj;
~修改表名
Alter tablr+biaoming rename 新表名;
~修改列名
Alter table +biaoming change uname username char(12);
4.刪除表
DROP TABLE 表名;
二、表的約束
1.單字段主鍵
create table student
(
xh char(12) PRIMARY KEY,
name char(12),
sex char(5),
age int
);
2.多字段主鍵
create table book3
(
ID int,
name char(8) not null, //not null爲非空約束
sex char(3) default '男',
ISBN char(20),
PRIMARY KEY(ID,ISBN)
);
3.字段值自動增加
create table book1
(
ID int auto_increment,
name char(20) not null,
shuhao int
);
create table student
(
xh char(12),
name char(12),
sex char(5),
age int
);
第三章 添加、更新與刪除數據
1.插入數據
insert into student(xh,name,sex,age,sdept)
values("201711059","吳樂娟","女","19","計科")
~可省略INTO
insert student (xh,name,sex,age,sdept)
values("2017110001","韓旭","女","19","計科")
~可省略各列名,但數據必須11對應
insert student values("201713031","徐佳瑩","女",”20”,"計科")
~一次添加多個數據
insert student values("201713015","邢家瑞","女",19,"計科"),
("201713042","谷聰","女",19,"計科"),
("201713043","趙晶","女",19,"計科")
2.修改數據(UPDATA)
UPDATE 表名
SET 字段名1 = 值1[,字段名2 = 值2,……][WHERE 更新條件]
~無條件時,全部有效
update student set age=18 where name="吳樂娟"
~修改多項,用逗號分隔
update student set age=16,sex="男" where name="谷聰"
3.刪除數據(DELETE)(truncate)
DELETE FROM 表名 [WHERE 條件表達式]
~ delete from student where age = 16
~'
delete from student where age = 20 and name="徐佳瑩"
//多條件時用and,or
~
//刪除表中所有記錄
~使用truncate刪除表中數據
truncate student
//只能刪除表中所有記錄