DDL语句 | 易学教程

创建表

CREATE TABLE

创建表的方法：
（1）直接创建

CREATE TABLE [IF NOT EXISTS] ‘tbl_name’ (col1 type1 修饰符, col2 type2 修饰符,
...)

#字段信息
col type1
PRIMARY KEY(col1,...)
INDEX(col1, ...)
UNIQUE KEY(col1, ...)

#表选项：
ENGINE [=] engine_name
ROW_FORMAT [=] {DEFAULT|DYNAMIC|FIXED|COMPRESSED|REDUNDANT|COMPACT}

例：

CREATE TABLE student (
id int UNSIGNED AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(20) NOT NULL,
age tinyint UNSIGNED,
gender ENUM('M','F') default 'M'
)ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;
#id字段以10初始值

DESC student;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type                 | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(20)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | NULL    |                |
| gender | enum('M','F')       | YES  |     | M       |                |
+--------+---------------------+------+-----+---------+----------------+
CREATE TABLE employee (id int UNSIGNED NOT NULL ,name VARCHAR(20) NOT NULL,age
tinyint UNSIGNED,PRIMARY KEY(id,name));

（2）通过查询现存表创建新表会被直接插入查询而来的数据

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name   [(create_definition,...)]  
[table_options]
[partition_options]   select_statement

例：

MariaDB [db1]> create table user select user,host,password from mysql.user;
Query OK, 4 rows affected (0.008 sec)
Records: 4 Duplicates: 0 Warnings: 0

MariaDB [db1]> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| student       |
| user          |
+---------------+
2 rows in set (0.000 sec)

MariaDB [db1]> desc user;
+----------+----------+------+-----+---------+-------+
| Field   | Type     | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| user     | char(80) | NO   |     |         |       |
| host     | char(60) | NO   |     |         |       |
| password | char(41) | NO   |     |         |       |
+----------+----------+------+-----+---------+-------+

（3）通过复制现存的表的表结构创建，但不复制数据

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name { LIKE old_tbl_name | (LIKE
old_tbl_name) }

例：

MariaDB [db1]> desc student;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(20)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | NULL    |                |
| gender | enum('M','F')       | YES  |     | M       |                |
+--------+---------------------+------+-----+---------+----------------+
4 rows in set (0.001 sec)

MariaDB [db1]> create table teacher like student;
Query OK, 0 rows affected (0.006 sec)

MariaDB [db1]> desc teacher;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(20)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | NULL    |                |
| gender | enum('M','F')       | YES  |     | M       |                |
+--------+---------------------+------+-----+---------+----------------+
4 rows in set (0.001 sec)

表查看

查看支持的engine

SHOW ENGINES；

查看表

SHOW TABLES [FROM db_name]

例：

MariaDB [db1]> show tables;
+---------------+
| Tables_in_db1 |
+---------------+
| student       |
+---------------+
1 row in set (0.000 sec)

查看表结构

DESC [db_name.]tb_name
SHOW COLUMNS FROM [db_name.]tb_name

例：

MariaDB [db1]> desc student;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(20)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | NULL    |                |
| gender | enum('M','F')       | YES  |     | M       |                |
+--------+---------------------+------+-----+---------+----------------+
4 rows in set (0.001 sec)

MariaDB [db1]> SHOW COLUMNS FROM student;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| name   | varchar(20)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | YES  |     | NULL    |                |
| gender | enum('M','F')       | YES  |     | M       |                |
+--------+---------------------+------+-----+---------+----------------+
4 rows in set (0.001 sec)

查看表创建命令

SHOW CREATE TABLE tbl_name

例：

MariaDB [db1]>show create table student;
+---------+---------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------+
| Table   | Create Table                                                        
                                                                               
                
                                   |
+---------+---------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------+
| student | CREATE TABLE `student` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
 `name` varchar(20) NOT NULL,
 `age` tinyint(3) unsigned DEFAULT NULL,
 `gender` enum('M','F') DEFAULT 'M',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=latin1 |
+---------+---------------------------------------------------------------------
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
-----------------------------------+
1 row in set (0.001 sec)

查看表状态

SHOW TABLE STATUS LIKE 'tbl_name’

例：

MariaDB [db1]> SHOW TABLE STATUS LIKE 'student'\G

*************************** 1. row ***************************
           Name: student
         Engine: InnoDB
         Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
     Data_length: 16384
 Max_data_length: 0
   Index_length: 0
       Data_free: 0
 Auto_increment: 10
     Create_time: 2020-02-17 11:35:29
     Update_time: NULL
     Check_time: NULL
       Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options:
         Comment:
Max_index_length: 0
       Temporary: N
1 row in set (0.001 sec)

查看库中所有表状态

SHOW TABLE STATUS FROM db_name

例：

MariaDB [db1]> SHOW TABLE STATUS FROM db1\G

*************************** 1. row ***************************
           Name: employee
         Engine: InnoDB
         Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
     Data_length: 16384
 Max_data_length: 0
   Index_length: 0
       Data_free: 0
 Auto_increment: NULL
     Create_time: 2020-02-17 11:43:21
     Update_time: NULL
     Check_time: NULL
       Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options:
         Comment:
Max_index_length: 0
       Temporary: N
       ......

修改和删除表

删除表

DROP TABLE [IF EXISTS] 'tbl_name';

修改表

ALTER TABLE 'tbl_name'
#字段：
#添加字段：add
ADD col1 data_type [FIRST|AFTER col_name]
#删除字段：drop
#修改字段：
alter（默认值）, change（字段名）, modify（字段属性）

修改表例：

ALTER TABLE students RENAME s1;
ALTER TABLE s1 ADD phone varchar(11) AFTER name;
ALTER TABLE s1 MODIFY phone int;
ALTER TABLE s1 CHANGE COLUMN phone mobile char(11);
ALTER TABLE s1 DROP COLUMN mobile;
ALTER TABLE s1 character set utf8;
ALTER TABLE s1 change name name varchar(20) character set utf8;
ALTER TABLE students ADD gender ENUM('m','f');
ALETR TABLE students CHANGE id sid int UNSIGNED NOT NULL PRIMARY KEY;
ALTER TABLE students DROP age;
DESC students;

#新建表无主键，添加和删除主键
CREATE TABLE t1 SELECT * FROM students;
ALTER TABLE t1 add primary key (stuid);
ALTER TABLE t1 drop primary key ;

来源：CSDN

作者：KanoeYuko

链接：https://blog.csdn.net/kanoeYuko/article/details/104466403

标签

table

mariadb

ddl

mysql