學習筆記9：MySQL語言（持續refreshing）

1.創建數據庫

mysql> show databases;

mysql> create database ranzai;

mysql> drop database ranzai;

mysql> select database();

mysql> use ranazi;

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2.查看數據引擎：

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+

3.查看錶

mysql> show tables;
Empty set (0.00 sec)//是個空表

數據表的數據類型

 

4.DDL 數據表

5.數據表操作：

1）主要操作：創建、修改、刪除；

2）定義信息：表名、字段名、字段類型；

6.MySQL的建表語法

Create [TEMPORARY] TABLE [IF NOT EXISIT]table_name[(create_definition,..)][table options][select_statemennt]

1）TEMPORARY：表示創建臨時表，在當前會話結束後自動消失；

2）IF NOT EXISIT：在建表之前，先判斷表是否存在，只有在表不存在的時候創建；

3）create_definition：建表語句的關鍵部分，用於定義表中各列的屬性；

4）table_option：表的配置選項，如表的默認存儲殷勤、字符集；

5）select_statemennt：通過select 語句建表

7.創建表

mysql> create table ran(
    ->     id int primary key,
    ->     name varchar (30),
    ->     phone varchar(11)
    ->  );
Query OK, 0 rows affected (0.28 sec)

8.更改表的結構 

1）添加字段

mysql> desc ran;//查看原表ran的數據結構
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   | PRI | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| phone | varchar(11) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

mysql> alter table ran add sex char(1);//對已經存在的表ran添加sex字段，數據類型爲char，限制爲1位
Query OK, 0 rows affected (0.35 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> desc ran;//查看新增字段後的表ran的數據結構
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int(11)     | NO   | PRI | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| phone | varchar(11) | YES  |     | NULL    |       |
| sex   | char(1)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+//新增了sex字段，數據類型爲char（1）
4 rows in set (0.01 sec)

2）修改字段數據類型

 alter table [表名] modify 字段 數據類型(位數);

mysql> alter table ran modify sex char(2);

3）刪除字段

 alter table [表名] drop column 字段;

mysql> alter table ran drop column sex;

4）刪除表

 drop table [表名];

mysql> drop table ran2;