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SQL语句
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): Can't 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_mode=NO_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`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
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
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