SQL语法基础之CREATE语句

　　　　　　　　　　　　　　　　SQL语法基础之CREATE语句

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　作者：尹正杰

一.查看帮助信息

1>.使用“？”来查看MySQL命令的帮助信息

mysql> ? CREATE 　　#这里告诉我们CREATE命令需要和那些命令一起使用

Many help items for your request exist.

To make a more specific request, please type 'help <item>',

where <item> is one of the following

topics:

   CREATE DATABASE

   CREATE EVENT

   CREATE FUNCTION

   CREATE FUNCTION UDF

   CREATE INDEX

   CREATE PROCEDURE

   CREATE RESOURCE GROUP

   CREATE ROLE

   CREATE SERVER

   CREATE SPATIAL REFERENCE SYSTEM

   CREATE TABLE

   CREATE TABLESPACE

   CREATE TRIGGER

   CREATE USER

   CREATE VIEW

   SHOW

   SHOW CREATE DATABASE

   SHOW CREATE EVENT

   SHOW CREATE FUNCTION

   SHOW CREATE PROCEDURE

   SHOW CREATE TABLE

   SHOW CREATE USER

   SPATIAL

mysql>

2>.查看CREATE DATABASE命令的帮助信息

mysql> ? CREATE DATABASE

Name: 'CREATE DATABASE'

Description:

Syntax:

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name

    [create_specification] ...

create_specification:

    [DEFAULT] CHARACTER SET [=] charset_name

  | [DEFAULT] COLLATE [=] collation_name

CREATE DATABASE creates a database with the given name. To use this

statement, you need the CREATE privilege for the database. CREATE

SCHEMA is a synonym for CREATE DATABASE.

URL: http://dev.mysql.com/doc/refman/8.0/en/create-database.html　　　　　　　　#这里是官方给的帮助文档

mysql>

3>.查询帮助时关键点剖析

　　刚刚学习MySQL的小伙伴，可能知道使用问好（“？”）可以查询命令的使用方法，但是获取到帮助信息后，看不懂该怎么用。别着急，我们把帮助信息细细的揣摩一下就明白咋用了，也方便我在下面执行相应的SQL语句时，大家不会产生过多歧义。首先我们以上面的查看“CREATE DATABASE”命令的帮助信息为例，简要说明一下该如何查看帮助信息：

　　第一：没有使用括号包裹起来的字段是必须写的。

　　第二：使用大括号（“{ }”）包裹起来的字段是必须写的，只不过我们需要从大括号中用管道（“|”）分隔的各个字段中选取相应一个来使用，例如“{DATABASE | SCHEMA}” 就表示我们必须选一个字段，要么选择DATABASE，要么选择SCHEME，不可以不选哟！

　　第三：中括号的字段是可以不写的，比如“[IF NOT EXISTS] ”这个语句咱们就是可以不写，不过建议大家写上，可以避免出错，它是一个IF判断语句。

二.CREATE DATABASE

1>.CREATE DATABASE 语句是在MySQL实力上创建一个指定名称的数据库，CREATE SCHEMA语句的语意和CREATE DATABASE是一样的。

mysql> ? CREATE DATABASE

Name: 'CREATE DATABASE'

Description:

Syntax:

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name

    [create_specification] ...

create_specification:

    [DEFAULT] CHARACTER SET [=] charset_name

  | [DEFAULT] COLLATE [=] collation_name

CREATE DATABASE creates a database with the given name. To use this

statement, you need the CREATE privilege for the database. CREATE

SCHEMA is a synonym for CREATE DATABASE.

URL: http://dev.mysql.com/doc/refman/8.0/en/create-database.html

mysql>

2>.当创建当数据本身存在没有写明“IF NOT EXISTS”子句是，创建数据库当语句会报错

3>.create_specification子句指明创建数据库的属性，并且存储在db.opt文件中

   • Character set属性指明此数据库的默认字符集

 
   • Collate属性指明此数据库的默认排序规则

4>.创建后的数据库在数据文件中所在目录会创建一个子句的文件目录，用来包含后续创建的表文件。

5>.创建数据库案例展示

mysql> SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

+--------------------+

4 rows in set (0.00 sec)

mysql>

mysql> CREATE DATABASE yinzhengjie CHARACTER SET = utf8;

Query OK, 1 row affected, 1 warning (0.01 sec)

mysql>

mysql> SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| yinzhengjie        |

+--------------------+

5 rows in set (0.00 sec)

mysql>

mysql> SHOW CREATE DATABASE yinzhengjie;

+-------------+----------------------------------------------------------------------+

| Database    | Create Database                                                      |

+-------------+----------------------------------------------------------------------+

| yinzhengjie | CREATE DATABASE `yinzhengjie` /*!40100 DEFAULT CHARACTER SET utf8 */ |

+-------------+----------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

创建一个默认字符集为utf8的数据库（mysql> CREATE DATABASE yinzhengjie CHARACTER SET = utf8;）

mysql> SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| yinzhengjie        |

+--------------------+

5 rows in set (0.00 sec)

mysql>

mysql> SHOW CREATE DATABASE yinzhengjie;

+-------------+----------------------------------------------------------------------+

| Database    | Create Database                                                      |

+-------------+----------------------------------------------------------------------+

| yinzhengjie | CREATE DATABASE `yinzhengjie` /*!40100 DEFAULT CHARACTER SET utf8 */ |

+-------------+----------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE DATABASE yinzhengjie CHARACTER SET = gbk;

ERROR 1007 (HY000): Can't create database 'yinzhengjie'; database exists

mysql>

mysql> CREATE DATABASE IF NOT EXISTS yinzhengjie CHARACTER SET = gbk;

Query OK, 1 row affected, 1 warning (0.00 sec)

mysql>

mysql> SHOW CREATE DATABASE yinzhengjie;

+-------------+----------------------------------------------------------------------+

| Database    | Create Database                                                      |

+-------------+----------------------------------------------------------------------+

| yinzhengjie | CREATE DATABASE `yinzhengjie` /*!40100 DEFAULT CHARACTER SET utf8 */ |

+-------------+----------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

创建数据库时，如果数据库存在就不创建，若不存在我们在创建，可避免MySQL的交互终端报错的情况！（mysql> CREATE DATABASE IF NOT EXISTS yinzhengjie CHARACTER SET = gbk;）

温馨提示：

    在MySQL5.7版本咱们也可以直接通过mkdir的操作系统命令在数据目录创建文件夹，则MySQL会识别为一个数据库，并在执行show databases命令时可以看到。

    但是，在MySQL8.0版本咱们再通过mkdir的操作系统命令在数据目录创建文件夹，就不会被识别了哟！

三.CREATE TABLE

1>.查看CREATE TABLE的帮助信息

mysql> ? CREATE TABLE

Name: 'CREATE TABLE'

Description:

Syntax:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    (create_definition,...)

    [table_options]

    [partition_options]

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    [(create_definition,...)]

    [table_options]

    [partition_options]

    [IGNORE | REPLACE]

    [AS] query_expression

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name

    { LIKE old_tbl_name | (LIKE old_tbl_name) }

create_definition:

    col_name column_definition

  | [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (key_part,...)

      [index_option] ...

  | {INDEX|KEY} [index_name] [index_type] (key_part,...)

      [index_option] ...

  | [CONSTRAINT [symbol]] UNIQUE [INDEX|KEY]

      [index_name] [index_type] (key_part,...)

      [index_option] ...

  | {FULLTEXT|SPATIAL} [INDEX|KEY] [index_name] (key_part,...)

      [index_option] ...

  | [CONSTRAINT [symbol]] FOREIGN KEY

      [index_name] (col_name,...) reference_definition

  | CHECK (expr)

column_definition:

    data_type [NOT NULL | NULL] [DEFAULT {literal | (expr)} ]

      [AUTO_INCREMENT] [UNIQUE [KEY]] [[PRIMARY] KEY]

      [COMMENT 'string']

      [COLUMN_FORMAT {FIXED|DYNAMIC|DEFAULT}]

      [reference_definition]

  | data_type [GENERATED ALWAYS] AS (expression)

      [VIRTUAL | STORED] [NOT NULL | NULL]

      [UNIQUE [KEY]] [[PRIMARY] KEY]

      [COMMENT 'string']

data_type:

    (see http://dev.mysql.com/doc/refman/8.0/en/data-types.html)

key_part: {col_name [(length)] | (expr)} [ASC | DESC]

index_type:

    USING {BTREE | HASH}

index_option:

    KEY_BLOCK_SIZE [=] value

  | index_type

  | WITH PARSER parser_name

  | COMMENT 'string'

  | {VISIBLE | INVISIBLE}

reference_definition:

    REFERENCES tbl_name (key_part,...)

      [MATCH FULL | MATCH PARTIAL | MATCH SIMPLE]

      [ON DELETE reference_option]

      [ON UPDATE reference_option]

reference_option:

    RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT

table_options:

    table_option [[,] table_option] ...

table_option:

    AUTO_INCREMENT [=] value

  | AVG_ROW_LENGTH [=] value

  | [DEFAULT] CHARACTER SET [=] charset_name

  | CHECKSUM [=] {0 | 1}

  | [DEFAULT] COLLATE [=] collation_name

  | COMMENT [=] 'string'

  | COMPRESSION [=] {'ZLIB'|'LZ4'|'NONE'}

  | CONNECTION [=] 'connect_string'

  | {DATA|INDEX} DIRECTORY [=] 'absolute path to directory'

  | DELAY_KEY_WRITE [=] {0 | 1}

  | ENCRYPTION [=] {'Y' | 'N'}

  | ENGINE [=] engine_name

  | INSERT_METHOD [=] { NO | FIRST | LAST }

  | KEY_BLOCK_SIZE [=] value

  | MAX_ROWS [=] value

  | MIN_ROWS [=] value

  | PACK_KEYS [=] {0 | 1 | DEFAULT}

  | PASSWORD [=] 'string'

  | ROW_FORMAT [=] {DEFAULT|DYNAMIC|FIXED|COMPRESSED|REDUNDANT|COMPACT}

  | STATS_AUTO_RECALC [=] {DEFAULT|0|1}

  | STATS_PERSISTENT [=] {DEFAULT|0|1}

  | STATS_SAMPLE_PAGES [=] value

  | TABLESPACE tablespace_name

  | UNION [=] (tbl_name[,tbl_name]...)

partition_options:

    PARTITION BY

        { [LINEAR] HASH(expr)

        | [LINEAR] KEY [ALGORITHM={1|2}] (column_list)

        | RANGE{(expr) | COLUMNS(column_list)}

        | LIST{(expr) | COLUMNS(column_list)} }

    [PARTITIONS num]

    [SUBPARTITION BY

        { [LINEAR] HASH(expr)

        | [LINEAR] KEY [ALGORITHM={1|2}] (column_list) }

      [SUBPARTITIONS num]

    ]

    [(partition_definition [, partition_definition] ...)]

partition_definition:

    PARTITION partition_name

        [VALUES

            {LESS THAN {(expr | value_list) | MAXVALUE}

            |

            IN (value_list)}]

        [[STORAGE] ENGINE [=] engine_name]

        [COMMENT [=] 'string' ]

        [DATA DIRECTORY [=] 'data_dir']

        [INDEX DIRECTORY [=] 'index_dir']

        [MAX_ROWS [=] max_number_of_rows]

        [MIN_ROWS [=] min_number_of_rows]

        [TABLESPACE [=] tablespace_name]

        [(subpartition_definition [, subpartition_definition] ...)]

subpartition_definition:

    SUBPARTITION logical_name

        [[STORAGE] ENGINE [=] engine_name]

        [COMMENT [=] 'string' ]

        [DATA DIRECTORY [=] 'data_dir']

        [INDEX DIRECTORY [=] 'index_dir']

        [MAX_ROWS [=] max_number_of_rows]

        [MIN_ROWS [=] min_number_of_rows]

        [TABLESPACE [=] tablespace_name]

query_expression:

    SELECT ...   (Some valid select or union statement)

CREATE TABLE creates a table with the given name. You must have the

CREATE privilege for the table.

By default, tables are created in the default database, using the

InnoDB storage engine. An error occurs if the table exists, if there is

no default database, or if the database does not exist.

For information about the physical representation of a table, see

http://dev.mysql.com/doc/refman/8.0/en/create-table-files.html.

URL: http://dev.mysql.com/doc/refman/8.0/en/create-table.html

mysql>

2>.基本的建表语句

mysql>

mysql> SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| yinzhengjie        |

+--------------------+

5 rows in set (0.00 sec)

mysql>

mysql> USE yinzhengjie;

Database changed

mysql>

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE TABLE student(stu_id int,stu_name varchar(30));

Query OK, 0 rows affected (0.01 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

+-----------------------+

1 row in set (0.00 sec)

mysql>

mysql> DESC student;

+----------+-------------+------+-----+---------+-------+

| Field    | Type        | Null | Key | Default | Extra |

+----------+-------------+------+-----+---------+-------+

| stu_id   | int(11)     | YES  |     | NULL    |       |

| stu_name | varchar(30) | YES  |     | NULL    |       |

+----------+-------------+------+-----+---------+-------+

2 rows in set (0.00 sec)

mysql>

在当前库中创建一个表（mysql> CREATE TABLE student(stu_id int,stu_name varchar(30));）

[root@node110 ~]# mysql -uroot -pyinzhengjie

mysql: [Warning] Using a password on the command line interface can be insecure.

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 11

Server version: 8.0.14 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

mysql> SHOW DATABASES;

+--------------------+

| Database           |

+--------------------+

| information_schema |

| mysql              |

| performance_schema |

| sys                |

| yinzhengjie        |

+--------------------+

5 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE IF NOT EXISTS yinzhengjie.student2(stu_id int,stu_name varchar(30));

Query OK, 0 rows affected (0.01 sec)

mysql>

mysql> SELECT DATABASE();

+------------+

| DATABASE() |

+------------+

| NULL       |

+------------+

1 row in set (0.00 sec)

mysql>

mysql> USE yinzhengjie

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>

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

+-----------------------+

2 rows in set (0.00 sec)

mysql> DESC student2;

+----------+-------------+------+-----+---------+-------+

| Field    | Type        | Null | Key | Default | Extra |

+----------+-------------+------+-----+---------+-------+

| stu_id   | int(11)     | YES  |     | NULL    |       |

| stu_name | varchar(30) | YES  |     | NULL    |       |

+----------+-------------+------+-----+---------+-------+

2 rows in set (0.00 sec)

mysql>

在指定的数据库中创建对应的表（mysql> CREATE TABLE IF NOT EXISTS yinzhengjie.student2(stu_id int,stu_name varchar(30)); ）

3>.TEMPORARY

　　注意，TEMPORARY关键字表示创建的是临时表，临时表仅对本链接可见，另外的数据库链接不可见，当本链接断开时，临时表也被自动DROP掉。

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

+-----------------------+

2 rows in set (0.00 sec)

mysql>

mysql> CREATE TEMPORARY TABLE student_temp(stu_tem_id int,stu_tem_name varchar(30));　　　　　　#这里我们使用TEMPORARY关键字创建了一张临时表

Query OK, 0 rows affected (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

+-----------------------+

2 rows in set (0.00 sec)

mysql> INSERT INTO student_temp VALUES(1,'jason');　　　　　　　　　　　　　　　　　　　　　　　　　　　　#我们往临时表中插入一条数据

Query OK, 1 row affected (0.00 sec)

mysql>

mysql> SELECT * FROM student_temp;　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　#很显然，数据往临时表中插入成功了，注意，如果此时另一个数据库链接在相同当数据库执行相同当查询语句是查不到数据当哟！能查询的仅限当前的数据库链接！

+------------+--------------+

| stu_tem_id | stu_tem_name |

+------------+--------------+

|          1 | jason        |

+------------+--------------+

1 row in set (0.00 sec)

mysql>

mysql>quit

Bye

[root@node110 ~]# mysql -uroot -pyinzhengjie

mysql: [Warning] Using a password on the command line interface can be insecure.

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 12

Server version: 8.0.14 MySQL Community Server - GPL

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> USE yinzhengjie

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>

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql> SELECT * FROM student_temp; 　　　　　　　　　　　　　　　　　　#很显然，当创建临时表当那个数据库链接端口后再链接，临时表已经不存在了！

ERROR 1146 (42S02): Table 'yinzhengjie.student_temp' doesn't exist

mysql>

mysql>

mysql> CREATE TEMPORARY TABLE student_temp(stu_tem_id int,stu_tem_name varchar(30));　　　　　　#这里我们使用TEMPORARY关键字创建了一张临时表

4>.LIKE

　　LIKE关键字表示基于另外一个表的定义复制一个新的空表，空表时尚的字段属性和索引都和原表相同。

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

+-----------------------+

2 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student3 LIKE student2;　　　　　　　　　　　　　　　　　　#咱们这里使用了LIKE关键字

Query OK, 0 rows affected (0.01 sec)

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

+-----------------------+

3 rows in set (0.00 sec)

mysql> DESC student2;

+----------+-------------+------+-----+---------+-------+

| Field    | Type        | Null | Key | Default | Extra |

+----------+-------------+------+-----+---------+-------+

| stu_id   | int(11)     | YES  |     | NULL    |       |

| stu_name | varchar(30) | YES  |     | NULL    |       |

+----------+-------------+------+-----+---------+-------+

2 rows in set (0.00 sec)

mysql>

mysql> DESC student3;

+----------+-------------+------+-----+---------+-------+

| Field    | Type        | Null | Key | Default | Extra |

+----------+-------------+------+-----+---------+-------+

| stu_id   | int(11)     | YES  |     | NULL    |       |

| stu_name | varchar(30) | YES  |     | NULL    |       |

+----------+-------------+------+-----+---------+-------+

2 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student3 LIKE student2;　　　　　　　　　　　　　　　　　　#咱们这里使用了LIKE关键字

mysql> SHOW CREATE TABLE student2;

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

| Table    | Create Table                                                                                                                          |

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

| student2 | CREATE TABLE `student2` (

  `stu_id` int(11) DEFAULT NULL,

  `stu_name` varchar(30) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW CREATE TABLE student3;

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

| Table    | Create Table                                                                                                                          |

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

| student3 | CREATE TABLE `student3` (

  `stu_id` int(11) DEFAULT NULL,

  `stu_name` varchar(30) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

+----------+---------------------------------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

mysql>

两张表的建表语句都相同哟！（mysql> SHOW CREATE TABLE student3;）

5>.CREATE TABLE ... AS SELECT 语句

　　表示创建表的同时将SELECT的查询结果数据插入到表中，但索引和主外键信息都不会同步过来

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

+-----------------------+

3 rows in set (0.00 sec)

mysql>

mysql> SELECT * FROM student;

+--------+-------------+

| stu_id | stu_name    |

+--------+-------------+

|      1 | jason       |

|      2 | danny       |

|      3 | jenny       |

|      4 | liming      |

|      5 | yinzhengjie |

+--------+-------------+

5 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student4 AS SELECT * FROM student;

Query OK, 5 rows affected (0.01 sec)

Records: 5  Duplicates: 0  Warnings: 0

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

+-----------------------+

4 rows in set (0.00 sec)

mysql>

mysql> SELECT * FROM student4;

+--------+-------------+

| stu_id | stu_name    |

+--------+-------------+

|      1 | jason       |

|      2 | danny       |

|      3 | jenny       |

|      4 | liming      |

|      5 | yinzhengjie |

+--------+-------------+

5 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student4 AS SELECT * FROM student;

6>.INNORE和REPLACE

　　表示在插入数据的过程中如果新表中碰到违反唯一约束的情况下怎么处理，IGNORE表示不插入，REPLACE表示替换已有的数据，默认两个关键字都不写则碰到违反的情况会报错。

7>.DATA_TYPE

　　表示定义字段类型

8>.NOT NULL/NULL

　　表示字段是否允许为空，默认NULL表示允许为空，NOT NULL表示需要对此字段明确数值，或者要有默认值，否则报错。

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

+-----------------------+

4 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student5(stu_id INT NOT NULL,stu_name VARCHAR(50));

Query OK, 0 rows affected (0.02 sec)

mysql>

mysql> INSERT INTO student5(stu_name) values('jason');                       #这里报错是正确的，因为我们要求stu_id字段不允许为空，我们又没有给他指定自增属性，因此需要手动给该字段赋值！

ERROR 1364 (HY000): Field 'stu_id' doesn't have a default value

mysql>

mysql> INSERT INTO student5(stu_id,stu_name) values(001,'jason');

Query OK, 1 row affected (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

+-----------------------+

5 rows in set (0.00 sec)

mysql>

mysql> SELECT * FROM student5;

+--------+----------+

| stu_id | stu_name |

+--------+----------+

|      1 | jason    |

+--------+----------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE TABLE student5(stu_id INT NOT NULL,stu_name VARCHAR(50));

9>.DEFAULT

　　表示设置字段的默认值

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

+-----------------------+

5 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student6(stu_id INT,stu_name varchar(50),stu_gender ENUM('boy','girl') DEFAULT 'boy');

Query OK, 0 rows affected (0.01 sec)

mysql>

mysql> INSERT INTO student6 VALUES(001,'yinzhengjie',DEFAULT);

Query OK, 1 row affected (0.01 sec)

mysql>

mysql> INSERT INTO student6 VALUES(002,'Jenny','girl');

Query OK, 1 row affected (0.00 sec)

mysql>

mysql> INSERT INTO student6(stu_id,stu_name) VALUES(003,'Danny');

Query OK, 1 row affected (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

+-----------------------+

6 rows in set (0.00 sec)

mysql> SELECT * FROM student6;

+--------+-------------+------------+

| stu_id | stu_name    | stu_gender |

+--------+-------------+------------+

|      1 | yinzhengjie | boy        |

|      2 | Jenny       | girl       |

|      3 | Danny       | boy        |

+--------+-------------+------------+

3 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student6(stu_id INT,stu_name varchar(50),stu_gender ENUM('boy','girl') DEFAULT 'boy');

10>.COLUMN_FORMAT

　　目前仅在ndb存储引擎的表上有用，表示该字段的存储类型是FIXED，DYNAMIC或者DEFAULT。

11>.STORAGE

　　目前也仅在ndb存储引擎的表上有用。

12>.CONSTRAINT

　　表示为主键，唯一键，外键等约束条件命名，如果没有命名则MySQL会默认给一个。

13>.PRIMARY KEY

　　表示该字段为主键，主键字段必须唯一，必须非空，一个表中只能有一个主键，主键可以包含一个或者多个字段。

14>.KEY/INDEX

　　表示索引字段。

15>.UNIQUE

　　表示该字段为唯一属性字段，且允许包含多个NULL值。

16>.FOREIGN KEY

　　表示该字段为外键字段。一个表中的 FOREIGN KEY 指向另一个表中的 PRIMARY KEY。

17>.AUTO_INCREMENT

　　表示字段为整数或者浮点数类型的value+1递增数值，value为当前表中该字段最大的值，默认是从1开始递增；一个表中只允许有一个自增字段，且该字段必须有key属性，不能还有DEFAULT属性，且插入复制会被当成很大的整数。

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

+-----------------------+

6 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student7(stu_id INT PRIMARY KEY AUTO_INCREMENT,stu_name VARCHAR(30));

Query OK, 0 rows affected (0.01 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

| student7              |

+-----------------------+

7 rows in set (0.00 sec)

mysql>

mysql> INSERT INTO student7(stu_name) VALUES('yinzhengjie');

Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO student7(stu_id,stu_name) VALUES(5,'jason');

Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student7(stu_name) VALUES('jenny');

Query OK, 1 row affected (0.01 sec)

mysql>

mysql> SELECT * FROM student7;

+--------+-------------+

| stu_id | stu_name    |

+--------+-------------+

|      1 | yinzhengjie |

|      5 | jason       |

|      6 | jenny       |

+--------+-------------+

3 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student7(stu_id INT PRIMARY KEY AUTO_INCREMENT,stu_name VARCHAR(30));

mysql> SELECT DATABASE();

+-------------+

| DATABASE()  |

+-------------+

| yinzhengjie |

+-------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

| student7              |

+-----------------------+

7 rows in set (0.01 sec)

mysql>

mysql> CREATE TABLE gender(

    ->  gender_id INT(11) NOT NULL,

    ->  name VARCHAR(30) DEFAULT NULL,

    ->  PRIMARY KEY(gender_id)

    -> );

Query OK, 0 rows affected (0.01 sec)

mysql>

创建gender表（mysql> CREATE TABLE gender( gender_id INT(11) NOT NULL, name VARCHAR(30) DEFAULT NULL, PRIMARY KEY(gender_id) );）

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| gender                |

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

| student7              |

+-----------------------+

8 rows in set (0.00 sec)

mysql>

mysql> CREATE TABLE student8(

    ->  stu_id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,

    ->  stu_name VARCHAR(50) UNIQUE,

    ->  gender INT,

    ->  CONSTRAINT  waijian_01 FOREIGN KEY(gender) REFERENCES gender(gender_id)

    -> );

Query OK, 0 rows affected (0.01 sec)

mysql> SHOW TABLES;

+-----------------------+

| Tables_in_yinzhengjie |

+-----------------------+

| gender                |

| student               |

| student2              |

| student3              |

| student4              |

| student5              |

| student6              |

| student7              |

| student8              |

+-----------------------+

9 rows in set (0.00 sec)

mysql>

 mysql> DESC student8;

+----------+-------------+------+-----+---------+----------------+

| Field    | Type        | Null | Key | Default | Extra          |

+----------+-------------+------+-----+---------+----------------+

| stu_id   | int(11)     | NO   | PRI | NULL    | auto_increment |

| stu_name | varchar(50) | YES  | UNI | NULL    |                |

| gender   | int(11)     | YES  | MUL | NULL    |                |

+----------+-------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

mysql>

mysql> DESC gender;

+-----------+-------------+------+-----+---------+-------+

| Field     | Type        | Null | Key | Default | Extra |

+-----------+-------------+------+-----+---------+-------+

| gender_id | int(11)     | NO   | PRI | NULL    |       |

| name      | varchar(30) | YES  |     | NULL    |       |

+-----------+-------------+------+-----+---------+-------+

2 rows in set (0.00 sec)

mysql>

mysql>

为student8创建外间约束（mysql> CREATE TABLE student8( stu_id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, stu_name VARCHAR(50) UNIQUE, gender INT, CONSTRAINT waijian_01 FOREIGN KEY(gender) REFERENCES gender(gender_id) );）

三.小试牛刀

设计一个学生选课数据库系统

　　　　• 创建一个名为course的数据库

　　　　• 在该数据库下创建以下几个表:

       　　• Students表:
　　　　　　　　　　sid整型自增主键，sname字符串64位，gender字符串12位，dept_id整型并外键到Dept表的id字段

　　　　　　• Dept表:
　　　　　　　　　　id整型自增主键，dept_name字符串64位

　　　　　　• Course表:
　　　　　　　　　　id整型自增字段主键，course_name字符串64位，teacher_id整型外键到 Teacher表的id字段

　　　　　　• Teacher表:
　　　　　　　　　　id整型自增字段主键，name字符串64位，dept_id整型外键到Dept表的id 字段

　　　　• Students表和teacher表的dept_id为非空

　　首先，上面这道题很简单，但是我要劝心急的小伙伴先把真道题读完了在写SQL，读完题之后我们会发现Student表依赖于Dept表，Course表依赖于Teacher表，Tearcher表依赖于Dept表，而这些表都存放在course的数据库中。分析清楚题意后我们在写SQL就相对得心应手了，相应的SQL语句如下：

mysql> CREATE DATABASE course CHARACTER SET = utf8;

Query OK, 1 row affected, 1 warning (0.00 sec)

mysql>

创建course数据库（mysql> CREATE DATABASE course CHARACTER SET = utf8;）

mysql> USE course;

Database changed

mysql>

mysql> CREATE TABLE Dept(id INT PRIMARY KEY AUTO_INCREMENT,demt_name VARCHAR(64));

Query OK, 0 rows affected (0.01 sec)

mysql>

创建Dept表（mysql> CREATE TABLE Dept(id INT PRIMARY KEY AUTO_INCREMENT,demt_name VARCHAR(64));）

mysql> select database();

+------------+

| database() |

+------------+

| course     |

+------------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE TABLE students(

    ->  sid INT PRIMARY KEY AUTO_INCREMENT,

    ->  sname VARCHAR(64),

    ->  gender VARCHAR(12),

    ->  dept_id INT NOT NULL,

    ->  CONSTRAINT student_dept FOREIGN KEY(dept_id) REFERENCES Dept(id)

    -> );

Query OK, 0 rows affected (0.01 sec)

mysql>

创建Student表（mysql> CREATE TABLE students( sid INT PRIMARY KEY AUTO_INCREMENT, sname VARCHAR(64), gender VARCHAR(12), dept_id INT NOT NULL, CONSTRAINT student_dept FOREIGN KEY(dept_id) REFERENCES Dept(id) );）

mysql> SELECT DATABASE();

+------------+

| DATABASE() |

+------------+

| course     |

+------------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE TABLE Teacher(

    ->  id INT PRIMARY KEY AUTO_INCREMENT,

    ->  name VARCHAR(64),

    ->  dept_id INT NOT NULL,

    ->  CONSTRAINT teacher_dept FOREIGN KEY(dept_id) REFERENCES Dept(id)

    -> );

Query OK, 0 rows affected (0.01 sec)

mysql>

创建Teacher表（ mysql> CREATE TABLE Teacher( id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(64), dept_id INT NOT NULL, CONSTRAINT teacher_dept FOREIGN KEY(dept_id) REFERENCES Dept(id) );）

mysql> SELECT DATABASE();

+------------+

| DATABASE() |

+------------+

| course     |

+------------+

1 row in set (0.00 sec)

mysql>

mysql> CREATE TABLE course(

    ->  id INT PRIMARY KEY AUTO_INCREMENT,

    ->  course_name VARCHAR(64),

    ->  teacher_id INT,

    ->  CONSTRAINT course_teacher FOREIGN KEY(teacher_id) REFERENCES Teacher(id)

    -> );

Query OK, 0 rows affected (0.01 sec)

mysql>

mysql>

创建course表（mysql> CREATE TABLE course( id INT PRIMARY KEY AUTO_INCREMENT, course_name VARCHAR(64), teacher_id INT, CONSTRAINT course_teacher FOREIGN KEY(teacher_id) REFERENCES Teacher(id) );）

mysql> SELECT DATABASE();

+------------+

| DATABASE() |

+------------+

| course     |

+------------+

1 row in set (0.00 sec)

mysql>

mysql> SHOW TABLES;

+------------------+

| Tables_in_course |

+------------------+

| Dept             |

| Teacher          |

| course           |

| students         |

+------------------+

4 rows in set (0.00 sec)

mysql>

mysql> DESC Dept;

+-----------+-------------+------+-----+---------+----------------+

| Field     | Type        | Null | Key | Default | Extra          |

+-----------+-------------+------+-----+---------+----------------+

| id        | int(11)     | NO   | PRI | NULL    | auto_increment |

| demt_name | varchar(64) | YES  |     | NULL    |                |

+-----------+-------------+------+-----+---------+----------------+

2 rows in set (0.00 sec)

mysql>

mysql> DESC Teacher;

+---------+-------------+------+-----+---------+----------------+

| Field   | Type        | Null | Key | Default | Extra          |

+---------+-------------+------+-----+---------+----------------+

| id      | int(11)     | NO   | PRI | NULL    | auto_increment |

| name    | varchar(64) | YES  |     | NULL    |                |

| dept_id | int(11)     | NO   | MUL | NULL    |                |

+---------+-------------+------+-----+---------+----------------+

3 rows in set (0.00 sec)

mysql> DESC course;

+-------------+-------------+------+-----+---------+----------------+

| Field       | Type        | Null | Key | Default | Extra          |

+-------------+-------------+------+-----+---------+----------------+

| id          | int(11)     | NO   | PRI | NULL    | auto_increment |

| course_name | varchar(64) | YES  |     | NULL    |                |

| teacher_id  | int(11)     | YES  | MUL | NULL    |                |

+-------------+-------------+------+-----+---------+----------------+

3 rows in set (0.01 sec)

mysql>

mysql> DESC students;

+---------+-------------+------+-----+---------+----------------+

| Field   | Type        | Null | Key | Default | Extra          |

+---------+-------------+------+-----+---------+----------------+

| sid     | int(11)     | NO   | PRI | NULL    | auto_increment |

| sname   | varchar(64) | YES  |     | NULL    |                |

| gender  | varchar(12) | YES  |     | NULL    |                |

| dept_id | int(11)     | NO   | MUL | NULL    |                |

+---------+-------------+------+-----+---------+----------------+

4 rows in set (0.00 sec)

mysql>

SQL语法基础之CREATE语句的更多相关文章

SQL语法基础之DROP语句
SQL语法基础之DROP语句作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.查看DROP帮助信息 mysql> ? DROP Many help items for yo ...
SQL语法基础之ALTER语句
SQL语法基础之ALTER语句作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.查看ALTER的帮助信息 mysql> ? ALTER Many help items fo ...
SQL语法基础之INSEART语句
SQL语法基础之INSEART语句作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.查看帮助信息 1>.查看INSERT方法的帮助信息 mysql> ? INSERT ...
SQL语法基础之UPDATE语句
SQL语法基础之UPDATE语句作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.查看UPDATE语句的帮助信息 1>.查看UPDATE的帮助信息 mysql> ? ...
SQL语法基础之DELETE语句
SQL语法基础之DELETE语句作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.查看帮助信息 1>.查看DELETE的帮助信息 mysql> ? DELETE Na ...
SQL语法基础之高级应用
SQL语法基础之高级应用作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.存储过程与函数 1>.CREATE PROCEDURE 用来创建存储过程 mysql> ? ...
SQL语法基础之SELECT
SQL语法基础之SELECT 作者:尹正杰版权声明:原创作品,谢绝转载!否则将追究法律责任. 一.SELECT查看帮助信息 1>.查看SELECT命令的帮助信息 mysql> ? SEL ...
SQL——语法基础篇（上）
用数据库的方式思考SQL是如何执行的虽然 SQL 是声明式语言,我们可以像使用英语一样使用它,不过在 RDBMS(关系型数据库管理系统)中,SQL 的实现方式还是有差别的.今天我们就从数据库的角度来 ...
oracle PL/SQL语法基础
目录数据类型定义变量 PL/SQL控制结构参考资料 Oracle10g数据类型总结 PL/SQL之基础篇数据类型学习总结字符类型 char.nchar.varchar.nvarchar:有 ...

随机推荐

微信web开发者工具移动调试
1 下载微信web开发者工具:https://mp.weixin.qq.com/wiki?t=resource/res_main&id=mp1455784140 下载一个自己能用的版本: 2 ...
HDU1505 City Game(算竞进阶习题)
写了1506顺便写下1505.. 还是求矩形面积,不过要预处理一下以每一个F为底的高度,然后想左右扩展到最大长度即为矩形的长.. 计算方法有点绕,令l[i]表示i的左边界,那么初始化l[i] = i. ...
shopNC 拓扑图
shopNC :
洛谷P4155 [SCOI2015]国旗计划（贪心，树形结构，基数排序）
洛谷题目传送门 \(O(n)\)算法来啦! 复杂度优化的思路是建立在倍增思路的基础上的,看看楼上几位巨佬的描述吧. 首先数组倍长是一样的.倍增法对于快速找到\(j\)满足\(l_j+m\le r_i\ ...
【BZOJ3653】谈笑风生（长链剖分）
[BZOJ3653]谈笑风生(长链剖分) 题面 BZOJ 洛谷权限题啊.... 题解首先根据题目给的条件,发现\(a,b\)都要是\(c\)的父亲. 所以这三个点是树上的一条深度单增的链. 因为\ ...
emwin之WM_DeleteWindow函数使用注意事项
@2018-12-21 [小记] 在当前窗口P创建一新窗口C后再使用函数 WM_DeleteWindow 删除该C窗口时,删除窗口句柄必须是根句柄,如果使用 WM_GetClientWindow(pM ...
SQL查询语句的进阶使用
MySQL的进阶使用 sql语句一些功能的使用导入现有大量数据文件步骤 1) 把*.sql文件拷贝到Linux某一位置(例如Desktop) 2) Linux命令行进入该位置 cd ~/Deskto ...
mybatis 二级缓存
Mybatis读取缓存次序: 先从二级缓存中获取数据,如果有直接获取,如果没有进行下一步: 从一级缓存中取数据,有直接获取,如果没有进行下一步: 到数据库中进行查询,并保存到一级缓存中: 当sqlSe ...
ajax 执行成功没有返回
提交表单或执行ajax 的按钮,只能使用 input type=“button” 标签
最全面的 Spring 学习笔记
http://www.codeceo.com/article/learn-spring.html 来源:泊浮目分享到:更多36 Spring致力于提供一种方法管理你的业务对象.在大量Java EE的 ...

SQL语法基础之CREATE语句

SQL语法基础之CREATE语句的更多相关文章

随机推荐

热门专题