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一、sql语句的语义种类
DDL: 数据定义语言 Data Definition Language
DCL: 数据控制语言 Data Control Language
DML: 数据操作语言 Data Manipulate Language
DQL: 数据查询语言 Data Query Language
二、DDL: 数据定义语言 create、drop
1.create针对库的操作
1语法
mysql help create database
Name: CREATE DATABASE
Description:
Syntax:
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name [create_specification] ...create_specification:[DEFAULT] CHARACTER SET [] charset_name | [DEFAULT] COLLATE [] collation_name
2创建库
mysql create database db1;
Query OK, 1 row affected (0.00 sec)mysql create SCHEMA db2;
Query OK, 1 row affected (0.00 sec)
3建库时提示已存在
mysql create database db1;
ERROR 1007 (HY000): Cant create database db1; database existsmysql create database IF NOT EXISTS db1;
Query OK, 1 row affected, 1 warning (0.00 sec)mysql create database IF NOT EXISTS db1;
Query OK, 1 row affected, 1 warning (0.00 sec)
4查看建库语句
mysql show create database db1;
--------------------------------------------------------------------------
| Database | Create Database |
--------------------------------------------------------------------------
| db1 | CREATE DATABASE db1 /*!40100 DEFAULT CHARACTER SET latin1 */ |
--------------------------------------------------------------------------
1 row in set (0.00 sec)
5创建数据库并指定字符集
mysql create database db3 charset utf8 COLLATE utf8_general_ci;
Query OK, 1 row affected (0.00 sec)mysql show create database db3;
------------------------------------------------------------------------
| Database | Create Database |
------------------------------------------------------------------------
| db3 | CREATE DATABASE db3 /*!40100 DEFAULT CHARACTER SET utf8 */ |
------------------------------------------------------------------------
1 row in set (0.00 sec)#不指定校验规则默认就是 utf8_general_ci
mysql create database db4 charset utf8;
Query OK, 1 row affected (0.00 sec)
6删库
mysql drop database db1;
Query OK, 0 rows affected (0.00 sec)
7修改库
mysql show create database db2; # 查看数据库使用字符集mysql alter database db2 charset utf8 collate utf8_general_ci; # 修改字符集
2.create针对表的操作
1语法
mysql help create table;
Name: CREATE TABLE
Description:
Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name(create_definition,...)[table_options][partition_options]CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name[(create_definition,...)][table_options][partition_options][IGNORE | REPLACE][AS] query_expressionCREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name{ LIKE old_tbl_name | (LIKE old_tbl_name) }
2建表
#1.进入一个库
mysql use db2#2.查看当前所在库
mysql select database();#3.建表建表最少有一列
mysql create table tb1;
ERROR 1113 (42000): A table must have at least 1 columnmysql create table tb1(id int);
Query OK, 0 rows affected (0.04 sec)#4.查看表
mysql show tables; # 查看库中有多少表mysql desc tb1; # 查看表中字段
3数据类型
int 整数 -2^31 - 2^31-1 (-2147483648 - 2147483647) 不能超出此范围
bigint 较大整数数据类型 -2^63 - 2^63-1 比int整数类型可用范围广
tinyint 最小整数 -128 - 127 #年龄 0 - 255
varchar 字符类型变长 #身份证
char 字符类型定长
enum 枚举类型 #给它固定选项只能选则选择项中的值 性别
datetime 时间类型 年月日时分秒
注意 如果使用datetime不是为now()当前时间而是直接书写时间如2020-03-01则需要在配置文件中添加此行信息sql_modeNO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
否则数据可能插入完成后并不会显示插入后的内容而是00-00-00.
4数据类型测试
#int类型
mysql create table tb1(id int); # 创建表名为tb1字段名为id类型为intmysql insert tb1 values(1); # 在tb1表中插入对应id字段的值为1
#enum类型
mysql create table qiudao(id int,sex enum(nan,nv));
Query OK, 0 rows affected (0.02 sec)mysql insert into qiudao values(1,nan);
Query OK, 1 row affected (0.00 sec)mysql insert into qiudao values(1,qiudao);
ERROR 1265 (01000): Data truncated for column sex at row 1
5建表测试
表名student
id
name
age
gender
cometime#1.建表
mysql create table student(- id int,- name varchar(12),- age tinyint,- gender enum(M,F),- cometime datetime);
Query OK, 0 rows affected (0.01 sec)#2.插入数据
mysql insert into student values(1,邱导,-18,M,now());
Query OK, 1 row affected (0.00 sec)
6建表数据属性
not null #非空
primary key #主键唯一且非空的
auto_increment #自增此列必须是primary key或者unique key
unique key #唯一键单独的唯一的
default #默认值
unsigned #非负数
comment #注释
7加上属性建表
#1.建表语句
create table students(
id int primary key auto_increment comment 学生id,
name varchar(12) not null comment 学生姓名,
age tinyint unsigned not null comment 学生年龄,
gender enum(M,F) default M comment 学生性别,
cometime datetime default now() comment 入学时间);#2.查看建表语句
mysql show create table students;
| students | CREATE TABLE students (id int(11) NOT NULL AUTO_INCREMENT COMMENT 学生id,name varchar(12) NOT NULL COMMENT 学生姓名,age tinyint(3) unsigned NOT NULL COMMENT 学生年龄,gender enum(M,F) DEFAULT M COMMENT 学生性别,cometime datetime DEFAULT CURRENT_TIMESTAMP COMMENT 入学时间,PRIMARY KEY (id)
) ENGINEInnoDB DEFAULT CHARSETutf8 |
1 row in set (0.00 sec)#3.插入数据
mysql insert into students values(1,qiudao,18,M,now());
Query OK, 1 row affected (0.00 sec)
#因为主键相同无法插入
mysql insert into students values(1,qiudao,18,M,now());
ERROR 1062 (23000): Duplicate entry 1 for key PRIMARY
#应该
mysql insert into students values(2,qiudao,18,M,now());
Query OK, 1 row affected (0.00 sec)
#主键已经设置自增没必要自己插入#正规插入数据的写法
mysql insert students(name,age) values(lhd,18);
Query OK, 1 row affected (0.00 sec)mysql insert students(name,age) values(lhd,12);
Query OK, 1 row affected (0.01 sec)mysql select * from students;
----------------------------------------------
| id | name | age | gender | cometime |
----------------------------------------------
| 1 | qiudao | 18 | M | 2020-07-14 19:51:44 |
| 2 | qiudao | 18 | M | 2020-07-14 19:52:19 |
| 3 | lhd | 18 | M | 2020-07-14 19:53:50 |
| 4 | lhd | 12 | M | 2020-07-14 19:53:58 |
----------------------------------------------
4 rows in set (0.00 sec)
3.删除表
drop table student;
4.修改表
#1.新建表
mysql create table linux(daijiadong tinyint);
Query OK, 0 rows affected (0.04 sec#2.修改表名
mysql alter table linux rename linux9;
Query OK, 0 rows affected (0.01 sec)#3.插入新字段
mysql alter table linux9 add rengyufeng int;
Query OK, 0 rows affected (0.14 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
---------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
---------------------------------------------------
| daijiadong | tinyint(4) | YES | | NULL | |
| rengyufeng | int(11) | YES | | NULL | |
---------------------------------------------------
2 rows in set (0.00 sec)#4.插入多个新字段
mysql alter table linux9 add liukong int,add wangzhangxing int;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
------------------------------------------------------
| daijiadong | tinyint(4) | YES | | NULL | |
| rengyufeng | int(11) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
------------------------------------------------------
4 rows in set (0.00 sec)#5.插入字段到最前面
mysql alter table linux9 add kangpeiwen varchar(100) first;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
--------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
--------------------------------------------------------
| kangpeiwen | varchar(100) | YES | | NULL | |
| daijiadong | tinyint(4) | YES | | NULL | |
| rengyufeng | int(11) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
--------------------------------------------------------
5 rows in set (0.01 sec)#6.插入字段到指定字段后面
mysql alter table linux9 add chenjianqing varchar(100) after daijiadong;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
--------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
--------------------------------------------------------
| kangpeiwen | varchar(100) | YES | | NULL | |
| daijiadong | tinyint(4) | YES | | NULL | |
| chenjianqing | varchar(100) | YES | | NULL | |
| rengyufeng | int(11) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
--------------------------------------------------------
6 rows in set (0.00 sec)#7.删除指定列
mysql alter table linux9 drop daijiadong;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
--------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
--------------------------------------------------------
| kangpeiwen | varchar(100) | YES | | NULL | |
| chenjianqing | varchar(100) | YES | | NULL | |
| rengyufeng | int(11) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
--------------------------------------------------------
5 rows in set (0.00 sec)#8.修改字段
mysql alter table linux9 change rengyufeng congtianqi int;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
--------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
--------------------------------------------------------
| kangpeiwen | varchar(100) | YES | | NULL | |
| chenjianqing | varchar(100) | YES | | NULL | |
| congtianqi | int(11) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
--------------------------------------------------------
5 rows in set (0.00 sec)#9.修改字段属性
mysql alter table linux9 modify congtianqi tinyint;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0mysql desc linux9;
--------------------------------------------------------
| Field | Type | Null | Key | Default | Extra |
--------------------------------------------------------
| kangpeiwen | varchar(100) | YES | | NULL | |
| chenjianqing | varchar(100) | YES | | NULL | |
| congtianqi | tinyint(4) | YES | | NULL | |
| liukong | int(11) | YES | | NULL | |
| wangzhangxing | int(11) | YES | | NULL | |
--------------------------------------------------------
5 rows in set (0.01 sec)
三、复制表结构
# 对数据库的表结构拷贝
mysql create table ttt like student; # 创建一个新的表叫ttt和student的表结构一致但不会将student的数据拷贝过来
Query OK, 0 rows affected (0.10 sec)# 对数据库数据拷贝
mysql insert into ttt select * from student; # 将查询出来的结果全部导入到ttt表中# 对导入数据筛选
mysql insert into ttt select * from student where age 22; # 对筛选结果导入到表ttt中
