PolarDB-X支持创建局部索引和全局二级索引 (Global Secondary Index，GSI) ，同时支持删除这两种索引。本语法仅适用于AUTO模式数据库。

局部索引

关于局部索引，详情请参见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,...)]
    [partition_options]
# 分区策略定义
partition_options:
    PARTITION BY
          HASH({column_name | partition_func(column_name)})
        | KEY(column_list)
        | RANGE{({column_name | partition_func(column_name)}) 
        | RANGE COLUMNS(column_list)}
        | LIST{({column_name | partition_func(column_name)}) 
        | LIST COLUMNS(column_list)} }
    partition_list_spec

# 分区函数定义
partition_func：
    YEAR
  | TO_DAYS
  | TO_SECOND
  | UNIX_TIMESTAMP
  | MONTH

# 分区列表定义
partition_list_spec:
    hash_partition_list
  | range_partition_list
  | list_partition_list

# Hash/Key分区表列定义
hash_partition_list:
    PARTITIONS partition_count

# Range/Range Columns分区表列定义
range_partition_list:
    range_partition [, range_partition ...]

range_partition:
    PARTITION partition_name VALUES LESS THAN {(expr | value_list)} [partition_spec_options]
    
# List/List Columns分区表列定义
list_partition_list:
    list_partition [, list_partition ...]

list_partition:
    PARTITION partition_name VALUES IN (value_list) [partition_spec_options]

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（DRDS模式）。

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。
# 先创建表
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 partition by hash(`order_id`) partitions 16;
# 再创建全局二级索引
CREATE GLOBAL INDEX `g_i_seller` ON t_order (`seller_id`) partition by hash(`seller_id`) partitions 16;
  • 主表：”t_order“是分区表，分区的拆分方式为按照”order_id“列进行哈希。
  • 索引表：”g_i_seller“按照”seller_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`) partition by hash(`seller_id`) partitions 16。

通过SHOW INDEX查看索引信息。

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。
show index from t_order;

返回信息如下：

+--------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table              | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| t_order_****_00000 |          0 | PRIMARY   |            1 | id          | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| t_order_****_00000 |          1 | l_i_order |            1 | order_id    | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------------------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.02 sec)
通过SHOW GLOBAL INDEX可以单独查看GSI信息，详情请参见SHOW GLOBAL INDEX。
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。
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 partition by hash(`seller_id`) partitions 16 |
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+