mySQL學習筆記二
阿新 • • 發佈:2020-01-23
DDL:操作資料庫,表
CRUD 操作資料庫
1.C(create):建立
2.R(Retrieve):查
3.U(Update) :修改
4.D(Delete):刪除
5.使用資料庫
mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | test | +--------------------+ 4 rows in set (0.00 sec) mysql> -- 前三個最好資料庫不要動
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> -- 檢視某個資料庫的字符集//建立語句 create database +資料庫名稱;
mysql> -- 建立資料庫如果不存在就建立,如果存在也不會報錯
mysql> create database if not exists db1;
Query OK,1 row affected (0.01 sec)
mysql> -- 建立db2在其不存在的情況下,並指定字符集為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> -- 刪除db3 mysql> drop database if exists db3; Query OK,0 rows affected,1 warning (0.00 sec)
mysql> -- 使用資料庫
mysql> -- 查詢當前正在使用的資料庫
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):建立
2.R(Retrieve):查
3.U(Update) :修改
4.D(Delete):刪除
mysql> create table 表名(
列名1 資料型別1,
列名2 資料型別2,
.....
列名n 資料型別n
);
mysql> -- 注意:最後一列不加逗號
mysql> /* 資料庫型別:1.int 整數型別: age int,2.double 小數型別: score double(5,2)
3.date: 日期,只包含年月日 yyyy-MM-dd
4.datetime:日期,年月日時分秒 yyyy-MM-dd
HH:mm:ss 如果將來不給這個欄位賦值,或者賦值為null,則預設使 用當前的系統時間,來自動賦值
5.timestamp 時間戳型別 包含年月日時分秒 yyyy-MM-dd HH:mm:ss 如果將來不給這個欄位賦值,或賦值為null,則預設使用當前的系統時間,來自動賦值
6.varchar:字串
* name varchar(20):姓名最大20個字元
*/
mysql> show tables;
mysql> -- desc是描述description的縮寫
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> -- 複製一下學生表
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,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> -- 新增一列
mysql> alter table stu add gender varchar(10);
Query OK,0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> -- 修改列名稱 型別
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,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> -- 刪除列
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)