局部索引
关于局部索引，详情清参见CREATE INDEX Statement。
全局二级索引
关于全局二级索引基本原理，请参见全局二级索引。
语法
CREATE [UNIQUE] GLOBAL INDEX index_name [index_type] ON tbl_name (index_sharding_col_name,...) global_secondary_index_option [index_option] [algorithm_option | lock_option] ... # 全局二级索引特有语法，具体说明请参见CREATE TABLE文档 global_secondary_index_option: [COVERING (col_name,...)] drds_partition_options # 分库分表子句，具体说明请参见CREATE TABLE文档 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] # length参数仅用于在索引表拆分键上创建局部索引 index_option: KEY_BLOCK_SIZE [=] value | index_type | WITH PARSER parser_name | COMMENT 'string' index_type: USING {BTREE | HASH} algorithm_option: ALGORITHM [=] {DEFAULT|INPLACE|COPY} lock_option: LOCK [=] {DEFAULT|NONE|SHARED|EXCLUSIVE}
CREATE 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。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。
关于全局二级索引定义子句详细说明，请参见CREATE TABLE。
示例
下面以建立普通全局二级索引为例，介绍在建表后创建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seller_id、id和order_id上的GSI，其中seller_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）。
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 | 1 | g_i_seller | 1 | seller_id | NULL | 0 | NULL | NULL | YES | GLOBAL | INDEX | | | t_order | 1 | g_i_seller | 2 | id | NULL | 0 | NULL | NULL | | GLOBAL | COVERING | | | t_order | 1 | g_i_seller | 3 | order_id | 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 | 1 | g_i_seller | seller_id | id, order_id | NULL | seller_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。
mysql> show create table g_i_seller; +------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | g_i_seller | CREATE TABLE `g_i_seller` ( `id` bigint(11) NOT NULL, `order_id` varchar(20) DEFAULT NULL, `seller_id` varchar(20) DEFAULT NULL, PRIMARY KEY (`id`), KEY `auto_shard_key_seller_id` (`seller_id`) USING BTREE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 dbpartition by hash(`seller_id`) | +------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
