技術標籤：mysql相關mysql學習

mysql資料庫和資料庫表操作語句學習筆記

資料庫操作語句

1.建立資料庫

creat database ‘資料庫名’

mysql> CREATE DATABASE test;
Query OK, 1 row affected (0.00 sec)

不過預設建立的資料庫編碼格式為latin1，在mysql中儲存和顯示中文時會產生亂碼

查詢資料庫編碼格式
mysql> show variables like 'character_set_database';
+------------------------+--------+
| Variable_name          | Value  |
+------------------------+--------+
| character_set_database | latin1 |
+------------------------+--------+
1 row in set (0.00 sec)

 

我們可以在建立資料庫的時候指定編碼格式
例如：

mysql> CREATE DATABASE test1 charset=utf8mb4;
Query OK, 1 row affected (0.00 sec)

另外資料庫不能重複建立，會報錯（ERROR 1007 (HY000): Can’t create database ‘test’; database exists）

2.檢視資料庫

mysql> show databases; 用來檢視所有資料庫
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
| test1              |
+--------------------+
6 rows in set (0.00 sec)
 

3.切換資料庫

選擇指定的資料庫
use
例如：

mysql> use test1;
Database changed

執行以上命令後，就選擇了test1這個資料庫，後續的操作都會在test1資料庫中進行操作

4.刪除資料庫

DROP DATABASE 語句用於刪除資料庫

mysql> drop database test;
Query OK, 0 rows affected (0.00 sec)


mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test1              |
+--------------------+
5 rows in set (0.00 sec)

 

5.修改資料庫

只能修改字符集

mysql> alter database test charset=utf8mb4;
Query OK, 1 row affected (0.00 sec)

表的操作語句

1.建立表

表由行和列組成，每個表都必須有個表名

CREATE TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
....
);

column_name 引數規定表中列的名稱。
data_type 引數規定列的資料型別（例如 varchar、integer、decimal、date 等等）。
size 引數規定表中列的最大長度。
例如：
建立一個學生表，包含三列，ID，姓名，年齡
在建立表之前要先進入到相應的資料庫中，在資料庫中建立表

mysql> use test1;
Database changed

mysql> show tables;
Empty set (0.00 sec)

mysql> create table student (id int ,name varchar(128),age int);
Query OK, 0 rows affected (0.02 sec)

id列和age列的資料型別是int，包含整數，name列的資料型別是varchar，包含字元

2.查詢表

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| student         |
+-----------------+
1 row in set (0.00 sec)

3.刪除表

DROP TABLE table_name

mysql> drop table student;
Query OK, 0 rows affected (0.03 sec)

mysql> show tables;
Empty set (0.00 sec)

補充：如果只刪除表內的資料，不刪除表本身，使用TRUNCATE TABLE語句

mysql> truncate table student;
Query OK, 0 rows affected (0.01 sec)

4.查詢表結構的詳細資訊

describe(或者desc)

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

5.查詢建表語句

show create table

mysql> show create table student;
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                                   |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
  `id` int(11) DEFAULT NULL,
  `name` varchar(128) DEFAULT NULL,
  `age` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

6.修改表

alter table 原表名 rename 新表名

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| student         |
+-----------------+
1 row in set (0.00 sec)

mysql> alter table student rename teacher;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| teacher         |
+-----------------+
1 row in set (0.00 sec)

也可以將表移動到另一個數據庫中
alter table rename to newdatabase.newtablename;
例如：將test1中的teacher表移動到test庫中 並取名為student

mysql> alter table teacher rename to test.student;
Query OK, 0 rows affected (0.00 sec)

mysql> show tables;
Empty set (0.00 sec)

mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| student        |
+----------------+
1 row in set (0.00 sec)

7.修改表字段

增加一個新欄位

alter table add 欄位名 資料型別 [屬性] ;
例：新增一個分數字段

mysql> alter table student add score float;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

增加一個新欄位，並放在首位

alter table add 欄位名 資料型別 [屬性] first ;
例：新增一個class欄位，並放到第一位

mysql> alter table student add class  int first ;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | int(11)      | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)

新增一個欄位，並放到指定欄位後面

alter table add 欄位名 資料型別 [屬性] after 指定欄位 ;
例：加一個aaa欄位 放到age後面

mysql> alter table student add aaa int after age ;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | int(11)      | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| aaa   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

修改欄位屬性

alter table modify 欄位名 資料型別 [屬性] ;
例：將原本class的int型別 改為varchar屬性 並限制最大長度為12

mysql> alter table student modify class varchar(12) ;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | varchar(12)  | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| aaa   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

修改欄位名

alter table change 原欄位名 新欄位名 資料型別 [屬性] ;
例：將aaa欄位改為 bbb欄位

mysql> alter table student change aaa bbb int;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | varchar(12)  | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| bbb   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

修改欄位位置

alter table change 原欄位名 新欄位名 資料型別 [屬性] after 指定欄位;
例：將bbb欄位改為ccc 並放到name後面

mysql> alter table student change bbb ccc  int after name;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | varchar(12)  | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| ccc   | int(11)      | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
6 rows in set (0.00 sec)

刪除欄位

alter table drop <欄位>
例：刪除ccc欄位

mysql> alter table student  drop ccc;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> describe student;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| class | varchar(12)  | YES  |     | NULL    |       |
| id    | int(11)      | YES  |     | NULL    |       |
| name  | varchar(128) | YES  |     | NULL    |       |
| age   | int(11)      | YES  |     | NULL    |       |
| score | float        | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
5 rows in set (0.00 sec)