ALTER TABLE

您可以通过ALTER TABLE语法改变表的结构,如增加列、增加索引、修改数据定义等。

注意事项

不支持通过ALTER TABLE语法修改拆分字段。

语法

说明 ALTER TABLE用于改变表的结构,如增加列、增加索引和修改数据定义。详细语法请参见MySQL修改表语法

ALTER [ONLINE|OFFLINE] [IGNORE] TABLE tbl_name
    [alter_specification [, alter_specification] ...]
  [partition_options]

示例

  • 增加列在"user_log"表中增加一列"idcard",示例如下:

    ALTER TABLE user_log
    ADD COLUMN idcard varchar(30);
    
  • 增加局部索引在"user_log"表中为"idcard"列增加一个名为"idcard_idx"的索引,示例如下:

    ALTER TABLE user_log
    ADD INDEX idcard_idx (idcard);
    
  • 重命名局部索引将"user_log"表中"idcard_idx"索引命修改为"idcard_idx_new",示例如下:

    ALTER TABLE user_log
    RENAME INDEX `idcard_idx` TO `idcard_idx_new`;
    
  • 删除局部索引删除"user_log"表中的"idcard_idx"索引,示例如下:

    ALTER TABLE user_log
    DROP INDEX idcard_idx;
    
  • 修改字段将"user_log"表中"idcard"列(字段类型为varchar)的长度由30改为40,语法示例如下:

    ALTER TABLE user_log
    MODIFY COLUMN idcard varchar(40);
    

全局二级索引

PolarDB-X支持全局二级索引 (Global Secondary Index, GSI),基本原理请参见全局二级索引

列变更

使用全局二级索引的表,对列的修改,语法和普通表的一致。 说明 当修改的表包含全局二级索引时,对列的修改有额外的限制,关于GSI的限制与约定,详情请参见如何使用全局二级索引

索引变更

语法

ALTER TABLE tbl_name
    alter_specification # 全局二级索引相关变更仅支持一条alter_specification
alter_specification:
  | ADD GLOBAL {INDEX|KEY} index_name # 全局二级索引必须显式指定索引名
      [index_type] (index_sharding_col_name,...)
      global_secondary_index_option
      [index_option] ...
  | ADD [CONSTRAINT [symbol]] UNIQUE GLOBAL
      [INDEX|KEY] index_name # 全局二级索引必须显式指定索引名
      [index_type] (index_sharding_col_name,...)
      global_secondary_index_option
      [index_option] ...
  | DROP {INDEX|KEY} index_name
  | RENAME {INDEX|KEY} old_index_name TO new_index_name
global_secondary_index_option:
    [COVERING (col_name,...)] # Covering Index
    drds_partition_options # 包含且仅包含index_sharding_col_name中指定的列
# 指定索引表拆分方式
drds_partition_options:
    DBPARTITION BY db_sharding_algorithm
    [TBPARTITION BY {table_sharding_algorithm} [TBPARTITIONS num]]
db_sharding_algorithm:
    HASH([col_name])
  | {YYYYMM|YYYYWEEK|YYYYDD|YYYYMM_OPT|YYYYWEEK_OPT|YYYYDD_OPT}(col_name)
  | UNI_HASH(col_name)
  | RIGHT_SHIFT(col_name, n)
  | RANGE_HASH(col_name, col_name, n)
table_sharding_algorithm: 
    HASH(col_name) 
  | {MM|DD|WEEK|MMDD|YYYYMM|YYYYWEEK|YYYYDD|YYYYMM_OPT|YYYYWEEK_OPT|YYYYDD_OPT}(col_name)
  | UNI_HASH(col_name)
  | RIGHT_SHIFT(col_name, n)
  | RANGE_HASH(col_name, col_name, n) 
# 以下为MySQL DDL语法
index_sharding_col_name:
    col_name [(length)] [ASC | DESC]
index_option:
    KEY_BLOCK_SIZE [=] value
  | index_type
  | WITH PARSER parser_name
  | COMMENT 'string'
index_type:
    USING {BTREE | HASH}

ALTER TABLE ADD GLOBAL INDEX系列语法用于在建表后添加GSI,该系列语法在MySQL语法上新引入了GLOBAL关键字,用于指定添加的索引类型为GSI。

ALTER TABLE { DROP | RENAME } INDEX语法同样可以对GSI进行修改,目前建表后创建GSI存在一定限制。关于GSI的限制与约定,详情请参见如何使用全局二级索引

全局二级索引定义子句详细说明请参见CREATE TABLE

示例

  • 建表后添加全局二级索引

    下面以建立全局唯一索引为例,介绍在建表后如何创建GSI。

    # 创建表
    CREATE TABLE t_order (
      `id` bigint(11) NOT NULL AUTO_INCREMENT,
      `order_id` varchar(20) DEFAULT NULL,
      `buyer_id` varchar(20) DEFAULT NULL,
      `seller_id` varchar(20) DEFAULT NULL,
      `order_snapshot` longtext DEFAULT NULL,
      `order_detail` longtext DEFAULT NULL,
      PRIMARY KEY (`id`),
      KEY `l_i_order` (`order_id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`order_id`);
    # 创建全局二级索引
    ALTER TABLE t_order ADD UNIQUE GLOBAL INDEX `g_i_buyer` (`buyer_id`) COVERING (`order_snapshot`) dbpartition by hash(`buyer_id`);
    
  • 主表:"t_order"只分库不分表,分库的拆分方式为按照"order_id"列进行哈希。

  • 索引表:"g_i_buyer"只分库不分表,分库的拆分方式为按照"buyer_id"列进行哈希,指定覆盖列为"order_snapshot"。

  • 索引定义子句:GLOBAL INDEX `g_i_seller` ON t_order (`seller_id`) dbpartition by hash(`seller_id`)

通过SHOW INDEX查看索引信息,包含拆分键order_id上的局部索引,和buyer_id、id、order_id和order_snapshot上的GSI,其中buyer_id为索引表的拆分键,id和order_id为默认的覆盖列(主键和主表的拆分键),order_snapshot显式指定的覆盖列。 说明 关于GSI的限制与约定,详情请参见如何使用全局二级索引,SHOW INDEX详细说明,请参见SHOW INDEX

  mysql> show index from t_order;
  +---------+------------+-----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
  | TABLE   | NON_UNIQUE | KEY_NAME  | SEQ_IN_INDEX | COLUMN_NAME    | COLLATION | CARDINALITY | SUB_PART | PACKED | NULL | INDEX_TYPE | COMMENT  | INDEX_COMMENT |
  +---------+------------+-----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
  | t_order |          0 | PRIMARY   |            1 | id             | A         |           0 |     NULL | NULL   |      | BTREE      |          |               |
  | t_order |          1 | l_i_order |            1 | order_id       | A         |           0 |     NULL | NULL   | YES  | BTREE      |          |               |
  | t_order |          0 | g_i_buyer |            1 | buyer_id       | NULL      |           0 |     NULL | NULL   | YES  | GLOBAL     | INDEX    |               |
  | t_order |          1 | g_i_buyer |            2 | id             | NULL      |           0 |     NULL | NULL   |      | GLOBAL     | COVERING |               |
  | t_order |          1 | g_i_buyer |            3 | order_id       | NULL      |           0 |     NULL | NULL   | YES  | GLOBAL     | COVERING |               |
  | t_order |          1 | g_i_buyer |            4 | order_snapshot | NULL      |           0 |     NULL | NULL   | YES  | GLOBAL     | COVERING |               |
  +---------+------------+-----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+----------+---------------+

通过SHOW GLOBAL INDEX可以单独查看GSI信息,详情请参见SHOW GLOBAL INDEX

  mysql> show global index from t_order;
  +---------------------+---------+------------+-----------+-------------+------------------------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+
  | SCHEMA              | TABLE   | NON_UNIQUE | KEY_NAME  | INDEX_NAMES | COVERING_NAMES               | INDEX_TYPE | DB_PARTITION_KEY | DB_PARTITION_POLICY | DB_PARTITION_COUNT | TB_PARTITION_KEY | TB_PARTITION_POLICY | TB_PARTITION_COUNT | STATUS |
  +---------------------+---------+------------+-----------+-------------+------------------------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+
  | ZZY3_DRDS_LOCAL_APP | t_order | 0          | g_i_buyer | buyer_id    | id, order_id, order_snapshot | NULL       | buyer_id         | HASH                | 4                  |                  | NULL                | NULL               | PUBLIC |
  +---------------------+---------+------------+-----------+-------------+------------------------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+

查看索引表的结构,索引表包含主表的主键、分库分表键、默认的覆盖列和自定义覆盖列,主键列去除了AUTO_INCREMENT属性,并且去除了主表中的局部索引,全局唯一索引默认在索引表的所有分库分表键上创建一个唯一索引,以实现全局唯一约束。

  mysql> show create table g_i_buyer;
  +-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table     | Create Table                                                                                                                                                                                                                                                                                                                 |
  +-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | g_i_buyer | CREATE TABLE `g_i_buyer` (`id` bigint(11) NOT NULL, `order_id` varchar(20) DEFAULT NULL, `buyer_id` varchar(20) DEFAULT NULL, `order_snapshot` longtext, PRIMARY KEY (`id`), UNIQUE KEY `auto_shard_key_buyer_id` (`buyer_id`) USING BTREE) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`buyer_id`)               |
  +-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  • 删除全局二级索引

    删除名为g_i_seller的GSI,相应的索引表也将被删除。

    # 删除索引
    ALTER TABLE `t_order` DROP INDEX `g_i_seller`;
    
  • 重命名索引

    默认情况下限制对GSI的重命名。关于GSI的限制与约定,详情请参见全局二级索引使用

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