MySQL表相关操作小结

备注:测试数据库版本为MySQL 8.0

这个blog我们来聊聊MySQL 表相关操作

一.创建表

语法:

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
  | {INDEX | KEY} [index_name] [index_type] (key_part,...)
      [index_option] ...
  | {FULLTEXT | SPATIAL} [INDEX | KEY] [index_name] (key_part,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] PRIMARY KEY
      [index_type] (key_part,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] UNIQUE [INDEX | KEY]
      [index_name] [index_type] (key_part,...)
      [index_option] ...
  | [CONSTRAINT [symbol]] FOREIGN KEY
      [index_name] (col_name,...)
      reference_definition
  | check_constraint_definition
}

column_definition: {
    data_type [NOT NULL | NULL] [DEFAULT {literal | (expr)} ]
      [AUTO_INCREMENT] [UNIQUE [KEY]] [[PRIMARY] KEY]
      [COMMENT 'string']
      [COLLATE collation_name]
      [COLUMN_FORMAT {FIXED | DYNAMIC | DEFAULT}]
      [STORAGE {DISK | MEMORY}]
      [reference_definition]
      [check_constraint_definition]
  | data_type
      [COLLATE collation_name]
      [GENERATED ALWAYS] AS (expr)
      [VIRTUAL | STORED] [NOT NULL | NULL]
      [UNIQUE [KEY]] [[PRIMARY] KEY]
      [COMMENT 'string']
      [reference_definition]
      [check_constraint_definition]
}

data_type:
    (see Chapter 11, Data Types)

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}
}

check_constraint_definition:
    [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED]

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 [STORAGE {DISK | MEMORY}]
  | 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)

MySQL的建表语句的语法太长了，看起来都觉得好麻烦
下面将建表的语法分解开

1.1 Table Name

类型	描述
Table Name	创建的表名称 举例: 1.tbl_name 2.db_name.tbl_name 3.’mydb'.’mytbl'
IF NOT EXISTS	如表名已存在 不报错

-- 用三种不同的表名的格式来创建表
create table t1(id int,name varchar(100));
create table test1.t2(id int,name varchar(100));
create table `test1`.`t3`(id int,name varchar(100));
-- 创建同名的表  if not exists未报错 有警告  且表为进行覆盖，依旧是原来的表
create table t1(id int,name varchar(100));
create table if not exists t1(id int,name varchar(100),type varchar(100));
show warnings\G
show create table t1\G

执行记录:

mysql> drop table t1,t2,t3;
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql>
mysql> -- 用三种不同的表名的格式来创建表
mysql> create table t1(id int,name varchar(100));
Query OK, 0 rows affected (0.02 sec)

mysql> create table test1.t2(id int,name varchar(100));
Query OK, 0 rows affected (0.02 sec)

mysql> create table `test1`.`t3`(id int,name varchar(100));
Query OK, 0 rows affected (0.02 sec)

mysql> -- 创建同名的表  if not exists未报错 有警告  且表为进行覆盖，依旧是原来的表
mysql> create table t1(id int,name varchar(100));
ERROR 1050 (42S01): Table 't1' already exists
mysql> create table if not exists t1(id int,name varchar(100),type varchar(100));
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> show warnings\G
*************************** 1. row ***************************
  Level: Note
   Code: 1050
Message: Table 't1' already exists
1 row in set (0.00 sec)

mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

1.2 Temporary Tables

MySQL的临时表与Oracle的全局临时表存在一定的差异
MySQL的临时表仅限当前的session有效，其它session即看不到表也看不到数据
InnoDB存储引擎不支持压缩的临时表
innodb_file_per-table 对临时表不会生效 临时表默认存储在 #innodb_temp 目录

-- session A:创建临时表
CREATE TEMPORARY TABLE new_tbl SELECT * FROM orig_tbl LIMIT 0;
show create table tmp_1\G
insert into tmp_1 (id,name) values (1,'abc');
select * from tmp_1;
-- session B: 查询临时表 提示表不存在
select * from tmp_1;

执行记录:

-- Session A:
mysql> create temporary table tmp_1(id int,name varchar(100));
Query OK, 0 rows affected (0.01 sec)

mysql> show create table tmp_1\G
*************************** 1. row ***************************
       Table: tmp_1
Create Table: CREATE TEMPORARY TABLE `tmp_1` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> insert into tmp_1 (id,name) values (1,'abc');
Query OK, 1 row affected (0.01 sec)

mysql> select * from tmp_1;
+------+------+
| id   | name |
+------+------+
|    1 | abc  |
+------+------+
1 row in set (0.00 sec)

-- Session B:
mysql> use test1;
Database changed
mysql>
mysql> select * from tmp_1;
ERROR 1146 (42S02): Table 'test1.tmp_1' doesn't exist

1.3 Table Cloning and Copying

表的克隆和拷贝

-- 建表，不拷贝数据  表结构和约束都会同时拷贝
CREATE TABLE new_tbl LIKE orig_tbl;
-- 建表，同时拷贝数据  表结构和数据会拷贝   表约束不会拷贝
CREATE TABLE new_tbl AS SELECT * FROM orig_tbl;

create table test1 (id int auto_increment primary key,name varchar(100));
insert into test1(name) values ('abc');
select * from test1;
show create table test1;
-- like拷贝表定义
create table t_like like test1;
select * from t_like;
show create table t_like;
-- ctas 拷贝数据，主键约束没有过来
create table t_ctas as select * from test1;
select * from test1;
show create table t_ctas;

执行记录:

mysql> create table test1 (id int auto_increment primary key,name varchar(100));
Query OK, 0 rows affected (0.03 sec)

mysql> insert into test1(name) values ('abc');
Query OK, 1 row affected (0.01 sec)

mysql>
mysql> select * from test1;
+----+------+
| id | name |
+----+------+
|  1 | abc  |
+----+------+
1 row in set (0.00 sec)

mysql>
mysql> show create table test1;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------+
| Table | Create Table
                    |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------+
| test1 | CREATE TABLE `test1` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------+
1 row in set (0.01 sec)

mysql>
mysql>
mysql>
mysql> create table t_like like test1;
Query OK, 0 rows affected (0.03 sec)

mysql> select * from t_like;
Empty set (0.01 sec)

mysql> show create table t_like;
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------
-----+
| Table  | Create Table
     |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------
-----+
| t_like | CREATE TABLE `t_like` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+------------------------------------------------------------------------------------------------------------------------------------------------------
-----+
1 row in set (0.00 sec)

mysql>
mysql>
mysql> create table t_ctas as select * from test1;
Query OK, 1 row affected (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select * from test1;
+----+------+
| id | name |
+----+------+
|  1 | abc  |
+----+------+
1 row in set (0.00 sec)

mysql>
mysql> show create table t_ctas;
+--------+----------------------------------------------------------------------------------------------------------------------------------+
| Table  | Create Table                                                                                                                     |
+--------+----------------------------------------------------------------------------------------------------------------------------------+
| t_ctas | CREATE TABLE `t_ctas` (
  `id` int NOT NULL DEFAULT '0',
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+----------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

1.4 Column Data Types and Attributes

类别	描述
data_type	列数据类型
NOT NULL or NULL	是否可以为空
DEFAULT	给列一个默认值
AUTO_INCREMENT	自动增长 当你insert一个null or 0 到一个自增列，会自动生产序列的下一个值
COMMENT	注释语句
COLUMN_FORMAT	列的格式(NDB)
STORAGE	存储(NDB)
GENERATED ALWAYS	基于现有列生产的列

-- 测试 not null、default、auto_increment、comment
create table user_info(id int primary key auto_increment comment '主键自增id',idcard varchar(50) not null comment '身份证号码',sex varchar(10) default '未知' comment '性别' );

show create table user_info\G

insert into user_info(id,idcard,sex) values(0,'123456','男');
insert into user_info(id,idcard,sex) values(null,'123456',null);
insert into user_info(id,idcard,sex) values(5,'123456','女');
-- insert的时候 没有指定  或者给null 和 0 的时候  自增列会是序列的下一个值
-- 当指定了之后，就是指定的值，而且序列的下一个值也会因为指定的这个值 而发生变化
select * from user_info;
-- 对于有指定default的列  给''/null 都不会触发默认值，只有录入的时候不指定列  才会触发default条件
insert into user_info(id,idcard,sex) values(null,'123456','');
insert into user_info(id,idcard) values(null,'123456');
select * from user_info;

执行记录:

mysql> create table user_info(id int primary key auto_increment comment '主键自增id',idcard varchar(50) not null comment '身份证号码',sex varchar(10) default '
未知' comment '性别' );
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql> show create table user_info\G
*************************** 1. row ***************************
       Table: user_info
Create Table: CREATE TABLE `user_info` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT '主键自增id',
  `idcard` varchar(50) NOT NULL COMMENT '身份证号码',
  `sex` varchar(10) DEFAULT '未知' COMMENT '性别',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql> insert into user_info(id,idcard,sex) values(0,'123456','男');
Query OK, 1 row affected (0.01 sec)

mysql> insert into user_info(id,idcard,sex) values(null,'123456',null);
Query OK, 1 row affected (0.01 sec)

mysql> insert into user_info(id,idcard,sex) values(5,'123456','女');
Query OK, 1 row affected (0.01 sec)

mysql> select * from user_info;
+----+--------+------+
| id | idcard | sex  |
+----+--------+------+
|  1 | 123456 | 男   |
|  2 | 123456 | NULL |
|  5 | 123456 | 女   |
+----+--------+------+
3 rows in set (0.00 sec)

mysql> insert into user_info(id,idcard,sex) values(null,'123456','');
Query OK, 1 row affected (0.01 sec)

mysql> select * from user_info;
+----+--------+------+
| id | idcard | sex  |
+----+--------+------+
|  1 | 123456 | 男   |
|  2 | 123456 | NULL |
|  5 | 123456 | 女   |
|  6 | 123456 |      |
+----+--------+------+
4 rows in set (0.00 sec)

mysql> insert into user_info(id,idcard) values(null,'123456');
Query OK, 1 row affected (0.01 sec)

mysql> select * from user_info;
+----+--------+---------+
| id | idcard | sex     |
+----+--------+---------+
|  1 | 123456 | 男      |
|  2 | 123456 | NULL    |
|  5 | 123456 | 女      |
|  6 | 123456 |         |
|  7 | 123456 | 未知    |
+----+--------+---------+
5 rows in set (0.00 sec)

GENERATED ALWAYS

CREATE TABLE t4 (
  first_name VARCHAR(10),
  last_name VARCHAR(10),
  full_name VARCHAR(255) AS (CONCAT(first_name,' ',last_name))
);

insert into t4(first_name,last_name) values ('马','云');
select * from t4;
insert into t4(first_name,last_name,'full_name') values ('马','化腾','马化腾');

执行记录:

mysql> CREATE TABLE t4 (
    ->   first_name VARCHAR(10),
    ->   last_name VARCHAR(10),
    ->   full_name VARCHAR(255) AS (CONCAT(first_name,' ',last_name))
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> insert into t4(first_name,last_name) values ('马','云');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t4;
+------------+-----------+-----------+
| first_name | last_name | full_name |
+------------+-----------+-----------+
| 马         | 云        | 马 云     |
+------------+-----------+-----------+
1 row in set (0.00 sec)

mysql> insert into t4(first_name,last_name,'full_name') values ('马','化腾','马化腾');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''full
_name') values ('马','化腾','马化腾')' at line 1
mysql>

1.5 Indexes, Foreign Keys, and CHECK Constraints

类别	描述
CONSTRAINT	约束
PRIMARY KEY	主键约束
KEY or INDEX	索引 key是index的同义词
UNIQUE	唯一约束
FULLTEXT	全文索引
SPATIAL	空间索引
FOREIGN KEY	外键
CHECK	检查约束
key_part	升序or降序 前缀
index_type	索引类别
index_option	KEY_BLOCK_SIZE、WITH PARSER、COMMENT
reference_definition	外键约束 指定主表的列

索引一般是创建表之后再创建，这个地方先略过，后面会单独写一个索引的blog

1.NOT NULL ：非空，用于保证该字段的值不能为空。
2.DEFAULT：默认值，用于保证该字段有默认值。
3.PRIMARY KEY：主键，用于保证该字段的值具有唯一性并且非空。
4.UNIQUE：唯一，用于保证该字段的值具有唯一性，可以为空。
5.CHECK：检查约束，检查字段的值是否为指定的值。
6.FOREIGN KEY：外键，用于限制两个表的关系，用于保证该字段的值必须来自于主表的关联列的值，在从表添加外键约束，用于引用主表中某些的值。

create table user_info
(id int primary key auto_increment comment '主键自增id',
 idcard varchar(50)  unique not null  comment '身份证号码'  ,
 sex varchar(10)  check(sex = '男' or sex = '女') default '男' comment '性别'
);

show create table user_info\G  
--
insert into user_info(id,idcard,sex) values (1,'123','abc');
insert into user_info(id,idcard,sex) values (0,'123','男');
insert into user_info(id,idcard,sex) values (0,'123','');
insert into user_info(id,idcard) values (0,'123');
insert into user_info(id,idcard) values (0,'456');

执行记录:

mysql> create table user_info
    -> (id int primary key auto_increment comment '主键自增id',
    ->  idcard varchar(50)  unique not null  comment '身份证号码'  ,
    ->  sex varchar(10)  check(sex = '男' or sex = '女') default '男' comment '性别'
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> show create table user_info\G
*************************** 1. row ***************************
       Table: user_info
Create Table: CREATE TABLE `user_info` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT '主键自增id',
  `idcard` varchar(50) NOT NULL COMMENT '身份证号码',
  `sex` varchar(10) DEFAULT '男' COMMENT '性别',
  PRIMARY KEY (`id`),
  UNIQUE KEY `idcard` (`idcard`),
  CONSTRAINT `user_info_chk_1` CHECK (((`sex` = _utf8mb3'男') or (`sex` = _utf8mb3'女')))
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql>
mysql>
-- 违反 检查约束
mysql> insert into user_info(id,idcard,sex) values (1,'123','abc');
ERROR 3819 (HY000): Check constraint 'user_info_chk_1' is violated.
-- 正常录入数据
mysql> insert into user_info(id,idcard,sex) values (0,'123','男');
Query OK, 1 row affected (0.01 sec)
--''一样也违反检查约束，并不会触发default值
mysql> insert into user_info(id,idcard,sex) values (0,'123','');
ERROR 3819 (HY000): Check constraint 'user_info_chk_1' is violated.
-- 违反idcard的唯一约束
mysql> insert into user_info(id,idcard) values (0,'123');
ERROR 1062 (23000): Duplicate entry '123' for key 'user_info.idcard'
mysql>
mysql>
-- 正常录入数据
mysql> insert into user_info(id,idcard) values (0,'456');
Query OK, 1 row affected (0.01 sec)

1.6 Table Options

类别	描述
ENGINE	指定存储引擎
AUTO_INCREMENT	自动增长
AVG_ROW_LENGTH	平均行长度
[DEFAULT] CHARACTER SET	指定字符集
CHECKSUM	MyISAM引擎独有的 快速查找损坏的表
[DEFAULT] COLLATE	指定的排序规则
COMMENT	表的备注
COMPRESSION	表压缩
CONNECTION	FEDERATED 存储引擎表 远程连接
DATA DIRECTORY, INDEX DIRECTORY	数据及索引目录
DELAY_KEY_WRITE	延迟更新索引到表关闭
ENCRYPTION	加密
INSERT_METHOD	Merge存储引擎独有
KEY_BLOCK_SIZE	index key blocks(MyISAM), 压缩表的page size(InnoDB)
MAX_ROWS	计划表录入最多的数据行数
MIN_ROWS	计划表录入最少的数据行数
PACK_KEYS	MyISAM独有
PASSWORD	未使用
ROW_FORMAT	指定数据行的物理存储
STATS_AUTO_RECALC	统计信息相关
STATS_PERSISTENT	统计信息相关
STATS_SAMPLE_PAGES	统计信息相关
TABLESPACE	表空间
UNION	仅在Merge存储引擎的时候生效

1.6.1 ENGINE

常见存储引擎 InnoDB、MyISAM、MEMORY、CSV、ARCHIVE、EXAMPLE、FEDERATED、HEAP、MERGE、NDB
MySQL 8.0之后，连系统表也有MyISAM改为InnoDB，InnoDB已经可以覆盖大部分应用场景了
其它的存储引擎也有各自的使用场景，后面单独写一个blog来简单介绍存储引擎。

1.6.2 AVG_ROW_LENGTH MAX_ROWS

用来控制行的长度和行的总数。

1.6.3 CHARACTER SET COLLATE

字符集和排序规则，MySQL 字符集和排序规则

1.6.4 COMMENT

表的备注，根据规范，表都需要有备注信息

1.6.5 COMPRESSION

表的压缩，节约空间，但是会消耗select 和DML语句的性能
适用于不会被访问的历史归档数据

1.6.6 STATS_AUTO_RECALC STATS_PERSISTENT STATS_SAMPLE_PAGES

STATS_PERSISTENT
指定是否为InnoDB表启用持久统计信息。

DEFAULT：表示表的持久统计信息设置由innodb_stats_persistent配置选项确定
1：表示启用表的持久统计信息
0：关闭此功能

STATS_AUTO_RECALC
指定是否自动重新计算InnoDB表的持久统计信息。

DEFAULT：表示表的持久统计信息设置由innodb_stats_auto_recalc配置选项确定
1：表示表中10％的数据发生更改时将重新计算统计信息
0：禁用自动重新计算此表

STATS_SAMPLE_PAGES
指定在估计索引列的基数和其他统计信息时要采样的索引页数

1.7 Table Partitioning

分区又是另外一个范畴了，会单独开一个blog，此处略过

二.修改表

语法:

ALTER TABLE tbl_name
    [alter_option [, alter_option] ...]
    [partition_options]

alter_option: {
    table_options
  | ADD [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | ADD [COLUMN] (col_name column_definition,...)
  | ADD {INDEX | KEY} [index_name]
        [index_type] (key_part,...) [index_option] ...
  | ADD {FULLTEXT | SPATIAL} [INDEX | KEY] [index_name]
        (key_part,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]] PRIMARY KEY
        [index_type] (key_part,...)
        [index_option] ...
  | ADD [CONSTRAINT [symbol]] UNIQUE [INDEX | KEY]
        [index_name] [index_type] (key_part,...)
        [index_option] ...
  | ADD [CONSTRAINT [symbol]] FOREIGN KEY
        [index_name] (col_name,...)
        reference_definition
  | ADD [CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED]
  | DROP {CHECK | CONSTRAINT} symbol
  | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED
  | ALGORITHM [=] {DEFAULT | INSTANT | INPLACE | COPY}
  | ALTER [COLUMN] col_name
        {SET DEFAULT {literal | (expr)} | DROP DEFAULT}
  | ALTER INDEX index_name {VISIBLE | INVISIBLE}
  | CHANGE [COLUMN] old_col_name new_col_name column_definition
        [FIRST | AFTER col_name]
  | [DEFAULT] CHARACTER SET [=] charset_name [COLLATE [=] collation_name]
  | CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]
  | {DISABLE | ENABLE} KEYS
  | {DISCARD | IMPORT} TABLESPACE
  | DROP [COLUMN] col_name
  | DROP {INDEX | KEY} index_name
  | DROP PRIMARY KEY
  | DROP FOREIGN KEY fk_symbol
  | FORCE
  | LOCK [=] {DEFAULT | NONE | SHARED | EXCLUSIVE}
  | MODIFY [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | ORDER BY col_name [, col_name] ...
  | RENAME COLUMN old_col_name TO new_col_name
  | RENAME {INDEX | KEY} old_index_name TO new_index_name
  | RENAME [TO | AS] new_tbl_name
  | {WITHOUT | WITH} VALIDATION
}

partition_options:
    partition_option [partition_option] ...

partition_option: {
    ADD PARTITION (partition_definition)
  | DROP PARTITION partition_names
  | DISCARD PARTITION {partition_names | ALL} TABLESPACE
  | IMPORT PARTITION {partition_names | ALL} TABLESPACE
  | TRUNCATE PARTITION {partition_names | ALL}
  | COALESCE PARTITION number
  | REORGANIZE PARTITION partition_names INTO (partition_definitions)
  | EXCHANGE PARTITION partition_name WITH TABLE tbl_name [{WITH | WITHOUT} VALIDATION]
  | ANALYZE PARTITION {partition_names | ALL}
  | CHECK PARTITION {partition_names | ALL}
  | OPTIMIZE PARTITION {partition_names | ALL}
  | REBUILD PARTITION {partition_names | ALL}
  | REPAIR PARTITION {partition_names | ALL}
  | REMOVE PARTITIONING
}

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}
}

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 [STORAGE {DISK | MEMORY}]
  | UNION [=] (tbl_name[,tbl_name]...)
}

partition_options:
    (see CREATE TABLE options)

2.1 修改表的存储引擎

语法:

-- 将非InnoDB存储引擎的表修改为 InnoDB存储引擎
ALTER TABLE t1 ENGINE = InnoDB;

测试记录:

mysql> create table t_5(id int,name varchar(100)) engine MyISAM;
Query OK, 0 rows affected (0.02 sec)

mysql>
mysql> show create table t_5\G
*************************** 1. row ***************************
       Table: t_5
Create Table: CREATE TABLE `t_5` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8
1 row in set (0.01 sec)

mysql> alter table t_5 engine InNODB;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t_5\G
*************************** 1. row ***************************
       Table: t_5
Create Table: CREATE TABLE `t_5` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

2.2 修改表自增值

语法:

-- 修改表的自增列值
ALTER TABLE t1 AUTO_INCREMENT = 13;

测试记录:

mysql> create table t5(id int primary key auto_increment,name varchar(100));
Query OK, 0 rows affected (0.03 sec)

mysql> insert into t5(id,name) values (0,'abc');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t5;
+----+------+
| id | name |
+----+------+
|  1 | abc  |
+----+------+
1 row in set (0.00 sec)

mysql> alter table t5 auto_increment = 99;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> insert into t5(id,name) values (0,'abc');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t5;
+----+------+
| id | name |
+----+------+
|  1 | abc  |
| 99 | abc  |
+----+------+
2 rows in set (0.00 sec)
-- 修改为比99小的10 居然没有报错
mysql> alter table t5 auto_increment = 10;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
-- 执行才知道  虽然修改语句没报错  但是木有生效
mysql> insert into t5(id,name) values (0,'abc');
Query OK, 1 row affected (0.01 sec)

mysql> select * from t5;
+-----+------+
| id  | name |
+-----+------+
|   1 | abc  |
|  99 | abc  |
| 100 | abc  |
+-----+------+
3 rows in set (0.00 sec)

2.3 修改表的字符集

语法:

-- 将表的字符集修改为utf8
ALTER TABLE t1 CHARACTER SET = utf8;

mysql> create table t6(id int,name varchar(100)) character set = utf8mb4;
Query OK, 0 rows affected (0.02 sec)

mysql> alter table t6 character set = utf8;
Query OK, 0 rows affected, 1 warning (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 1

2.4 修改表的备注信息

语法:

-- 修改表备注信息
ALTER TABLE t1 COMMENT = 'New table comment';

测试记录:

mysql> create table t7(id int,name varchar(100)) comment 'old comment';
Query OK, 0 rows affected (0.03 sec)

mysql> show create table t7\G
*************************** 1. row ***************************
       Table: t7
Create Table: CREATE TABLE `t7` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='old comment'
1 row in set (0.00 sec)

mysql> alter table t7 comment = 'new comment';
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t7\G
*************************** 1. row ***************************
       Table: t7
Create Table: CREATE TABLE `t7` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='new comment'
1 row in set (0.00 sec)

2.5 重命名、重新定义和重新排序列

1.change
可以重命名或重定义列，或者两者一起
2.modify
修改列定义，但是不能修改列名
对于修改列定义而言，比change更方便
3.rename
可以重命名列，但是不能修改列的定义
对于重命名而言，比change更方便

语法:

-- 将列调整为非空
ALTER TABLE t1 MODIFY b INT NOT NULL;
-- 将列名由b修改为a
ALTER TABLE t1 RENAME COLUMN b TO a;
-- 修改col1列的定义
ALTER TABLE t1 MODIFY col1 BIGINT UNSIGNED DEFAULT 1 COMMENT 'my column';

测试记录:

mysql> create table t8(id int,name1 varchar(10));
Query OK, 0 rows affected (0.03 sec)

mysql>
mysql> alter table t8 modify id int not null;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table t8 rename column name1 to name;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql>
mysql> alter table t8 modify id bigint unsigned default 1 comment 'my column';
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> show create table t8\G
*************************** 1. row ***************************
       Table: t8
Create Table: CREATE TABLE `t8` (
  `id` bigint unsigned DEFAULT '1' COMMENT 'my column',
  `name` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql>

2.6 约束相关

`语法:

-- 删除主键约束
ALTER TABLE tbl_name DROP PRIMARY KEY;
-- 新增约束
ALTER TABLE tbl_name
    ADD CONSTRAINT [symbol] CHECK (expr) [[NOT] ENFORCED];
-- 删除约束
ALTER TABLE tbl_name
    DROP CONSTRAINT symbol;

ALTER TABLE tbl_name
    DROP CHECK symbol;

测试记录:

mysql> create table t9(id int primary key,name1 varchar(10));
Query OK, 0 rows affected (0.02 sec)

mysql> show create table t9\G
*************************** 1. row ***************************
       Table: t9
Create Table: CREATE TABLE `t9` (
  `id` int NOT NULL,
  `name1` varchar(10) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql>
mysql> alter table t9 drop primary key;
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> alter table t9 add unique u1(name1);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t9\G
*************************** 1. row ***************************
       Table: t9
Create Table: CREATE TABLE `t9` (
  `id` int NOT NULL,
  `name1` varchar(10) DEFAULT NULL,
  UNIQUE KEY `u1` (`name1`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)
mysql> alter table t9 drop constraint u1;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

2.7 修改表和列的字符集

语法:

-- 修改表默认的字符集
ALTER TABLE tbl_name DEFAULT CHARACTER SET charset_name;
-- 修改列的字符集
ALTER TABLE t MODIFY latin1_text_col TEXT CHARACTER SET utf8;

测试记录:

mysql> create table t10(id int,name varchar(100));
Query OK, 0 rows affected (0.03 sec)

mysql> show create table t10\G
*************************** 1. row ***************************
       Table: t10
Create Table: CREATE TABLE `t10` (
  `id` int DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

mysql>
mysql>
mysql> alter table t10 default character set utf8mb4;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table t10\G
*************************** 1. row ***************************
       Table: t10
Create Table: CREATE TABLE `t10` (
  `id` int DEFAULT NULL,
  `name` varchar(100) CHARACTER SET utf8 DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

mysql>
mysql>
mysql>
mysql> alter table t10 modify name varchar(100) character set utf8;
Query OK, 0 rows affected, 1 warning (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 1

三.删除表

语法:

DROP [TEMPORARY] TABLE [IF EXISTS]
    tbl_name [, tbl_name] ...
    [RESTRICT | CASCADE]

测试记录:

mysql> drop table t1;
Query OK, 0 rows affected (0.02 sec)

mysql> drop table t11;
ERROR 1051 (42S02): Unknown table 'test1.t11'
mysql>
mysql>
mysql> drop table if exists t11;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql>
mysql> show warnings;
+-------+------+---------------------------+
| Level | Code | Message                   |
+-------+------+---------------------------+
| Note  | 1051 | Unknown table 'test1.t11' |
+-------+------+---------------------------+
1 row in set (0.00 sec)

mysql>

mysql>
mysql> drop table t2,t3,t4,t5,t6,t7,t8,t9,t10;
Query OK, 0 rows affected (0.08 sec)