大二下第二週週三學習記錄

MySQL資料模型

二、SQL

（1）SQL簡介

（2）SQL通用語法

（3）SQL分類

（4）DDL

1. ddl對資料庫的操作

mysql> create database if not exists db2;
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> drop database db2;
Query OK, 0 rows affected (0.04 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| ceyan              |
| db3                |
| eshop              |
| information_schema |
| meetingsystem      |
| mysql              |
| performance_schema |
| runoob             |
| selectcource       |
| student            |
| sys                |
| users              |
| web_test           |
+--------------------+
13 rows in set (0.00 sec)

mysql> drop database if exists db2;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> use db3;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| db3        |
+------------+
1 row in set (0.00 sec)
 

2. DDL對錶的操作

mysql> show tables;
+---------------+
| Tables_in_db3 |
+---------------+
| db3           |
| uuu           |
+---------------+
2 rows in set (0.01 sec)

mysql> desc db3;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| name  | varchar(20) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
1 row in set (0.01 sec)
 

mysql> create table eee(
    -> id int ,
    -> username varchar(20),
    -> password varchar(32)
    -> );
Query OK, 0 rows affected (0.06 sec)

mysql> desc eee;
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id       | int         | YES  |     | NULL    |       |
| username | varchar(20) | YES  |     | NULL    |       |
| password | varchar(32) | YES  |     | NULL    |       |
+----------+-------------+------+-----+---------+-------+
3 rows in set (0.02 sec)
 

MySQL資料型別

mysql> drop table if exists eee;
Query OK, 0 rows affected (0.06 sec)

mysql> show tables;
+---------------+
| Tables_in_db3 |
+---------------+
| db3           |
| uuu           |
+---------------+
2 rows in set (0.01 sec)