MySQL ALTER TABLE语法

先看一下定义（密密麻麻）

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

alter_specification:
    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 check_constraint_definition
  | DROP CHECK symbol
  | ALTER CHECK symbol [NOT] ENFORCED
  | ALGORITHM [=] {DEFAULT|INSTANT|INPLACE|COPY}
  | ALTER [COLUMN] col_name {SET DEFAULT literal | 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}

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

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)

实际上也不复杂，一条一条看，就看懂了。我介绍一些常用的：

测试表

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;

1. 重置自增值

ALTER TABLE `user` AUTO_INCREMENT = 15
> OK
> 时间: 0.013s

2. 更改字符集

ALTER TABLE `user` CHARACTER SET = utf8;

3. 更改表注释

ALTER TABLE `user` COMMENT = 'New table comment';

4. 添加列

ALTER TABLE `user` ADD COLUMN create_time datetime NOT NULL
> OK
> 时间: 0.057s

5. 删除列

ALTER TABLE `user` DROP COLUMN create_time
> OK
> 时间: 0.046s

如果要单个语句删除多个列

ALTER TABLE `user` DROP COLUMN col_1, DROP COLUMN col_2;

6. 重新定义列

CHANGE

-- 可以重命名列并更改其定义，或两者。
-- 具有比MODIFY或 更多的能力RENAME COLUMN，但是以某些操作的便利性为代价。CHANGE 如果不重命名，则需要将列命名两次，如果仅重命名，则需要重新指定列定义。
-- 使用FIRST或AFTER可以重新排序列。
ALTER TABLE `user` CHANGE create_time create_time int NOT NULL AFTER id;

MODIFY

-- 可以更改列定义但不能更改其名称。
-- 比CHANGE不更改列定义的情况下，更改列定义更方便，因为不用命名两次。
-- 使用FIRST或AFTER可以重新排序列。
ALTER TABLE `user` MODIFY create_time char(32) NOT NULL FIRST;

RENAME

-- 可以更改列名但不能更改其定义。
-- 比CHANGE重命名列而不更改其定义的情况下更方便。
ALTER TABLE `user` RENAME COLUMN create_time TO order_id;

这个在MySQL5.X是不行的，如下：

ALTER TABLE `user` RENAME COLUMN create_time TO order_id
> 1064 - 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 'COLUMN create_time TO order_id' at line 11
> 时间: 0s

但是在MySQL8.X是可以的（我在Docker上创建一个8.X的容器）

查看表结构