标签：set mySQL 笔记 学习 stu sec mysql YES NULL
DDL：操作数据库，表
CRUD 操作数据库
1.C（create）：创建
2.R（Retrieve)：查
3.U（Update) :修改
4.D（Delete）：删除
5.使用数据库
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set (0.00 sec)
mysql> -- 前三个最好数据库不要动
mysql> show create database mysql;
+----------+----------------------------------------------------------------+
| Database | Create Database |
+----------+----------------------------------------------------------------+
| mysql | CREATE DATABASE `mysql` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+----------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> -- 查看某个数据库的字符集//创建语句 create database +数据库名称；
mysql> -- 创建数据库如果不存在就创建，如果存在也不会报错
mysql> create database if not exists db1;
Query OK, 1 row affected (0.01 sec)
mysql> -- 创建db2在其不存在的情况下，并指定字符集为gbk
mysql> create database if not exists db2 character set gbk;
Query OK, 1 row affected (0.00 sec)
mysql> -- 修改字符集
mysql> alter database db2 character set utf8;
Query OK, 1 row affected (0.00 sec)
mysql> -- 删除db3
mysql> drop database if exists db3;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> -- 使用数据库
mysql> -- 查询当前正在使用的数据库
mysql> select database();
+------------+
| database() |
+------------+
| NULL |
+------------+
1 row in set (0.00 sec)
mysql> use db2;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| db2 |
+------------+
1 row in set (0.00 sec)
CRUD 操作表
1.C（create）：创建
2.R（Retrieve)：查
3.U（Update) :修改
4.D（Delete）：删除
mysql> create table 表名(
列名1 数据类型1，
列名2 数据类型2，
.....
列名n 数据类型n
);
mysql> -- 注意：最后一列不加逗号
mysql> /* 数据库类型：1.int 整数类型： age int,
2.double 小数类型： score double(5, 2)
3.date： 日期，只包含年月日 yyyy-MM-dd
4.datetime:日期，年月日时分秒 yyyy-MM-dd
HH:mm:ss 如果将来不给这个字段赋值，或者赋值为null，则默认使 用当前的系统时间，来自动赋值
5.timestamp 时间戳类型 包含年月日时分秒 yyyy-MM-dd HH:mm:ss 如果将来不给这个字段赋值，或赋值为null，则默认使用当前的系统时间，来自动赋值
6.varchar:字符串
* name varchar(20):姓名最大20个字符
*/
mysql> show tables;
mysql> -- desc是描述description的缩写
mysql> desc 表名;
mysql> create table student(
-> id int,
-> name varchar(32),
-> age int,
-> score double(4,1),
-> birthday date,
-> insert_time timestamp
-> );
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| student |
+---------------+
1 row in set (0.00 sec)
mysql> desc student;
+-------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| score | double(4,1) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| insert_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------+-------------+------+-----+-------------------+-----------------------------+
6 rows in set (0.02 sec)
mysql> -- 复制一下学生表
mysql> create table stu like student;
Query OK, 0 rows affected (0.01 sec)
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| stu |
| student |
+---------------+
2 rows in set (0.00 sec)
mysql> desc stu;
+-------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| score | double(4,1) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| insert_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------+-------------+------+-----+-------------------+-----------------------------+
6 rows in set (0.01 sec)
mysql> drop table stu;
Query OK, 0 rows affected (0.00 sec)
mysql> drop table stu;
ERROR 1051 (42S02): Unknown table 'stu'
mysql> drop table if exists stu;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> -- 修改表的字符集
mysql> alter table stu character set utf8;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| stu |
+---------------+
1 row in set (0.00 sec)
mysql> -- 添加一列
mysql> alter table stu add gender varchar(10);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> -- 修改列名称 类型
mysql> alter table stu change gender sex varchar(20);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| stu |
+---------------+
1 row in set (0.00 sec)
mysql> desc stu;
+-------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| score | double(4,1) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| insert_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| sex | varchar(20) | YES | | NULL | |
+-------------+-------------+------+-----+-------------------+-----------------------------+
7 rows in set (0.02 sec)
mysql> alter table stu modify sex varchar(10);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| stu |
+---------------+
1 row in set (0.00 sec)
mysql> desc stu;
+-------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| score | double(4,1) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| insert_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| sex | varchar(10) | YES | | NULL | |
+-------------+-------------+------+-----+-------------------+-----------------------------+
7 rows in set (0.02 sec)
mysql> -- 删除列
mysql> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| stu |
+---------------+
1 row in set (0.00 sec)
mysql> desc stu;
+-------------+-------------+------+-----+-------------------+-----------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+-------------+------+-----+-------------------+-----------------------------+
| id | int(11) | YES | | NULL | |
| name | varchar(32) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| score | double(4,1) | YES | | NULL | |
| birthday | date | YES | | NULL | |
| insert_time | timestamp | NO | | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+-------------+-------------+------+-----+-------------------+-----------------------------+
6 rows in set (0.02 sec)
只不停
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标签：set,mySQL,笔记,学习,stu,sec,mysql,YES,NULL 来源： https://blog.csdn.net/weixin_42082088/article/details/104075751
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