PolarDB-X支持創(chuàng)建局部索引和全局二級(jí)索引 (Global Secondary Index, GSI) ，同時(shí)支持刪除這兩種索引。本語法僅適用于DRDS模式數(shù)據(jù)庫。

局部索引

關(guān)于局部索引，詳情請(qǐng)參見CREATE INDEX Statement。

全局二級(jí)索引

關(guān)于全局二級(jí)索引基本原理，請(qǐng)參見全局二級(jí)索引。

語法

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] ...

# 全局二級(jí)索引特有語法，具體說明請(qǐng)參見CREATE TABLE文檔
global_secondary_index_option:
    [COVERING (col_name,...)]
    drds_partition_options
    [VISIBLE|INVISIBLE]

# 分庫分表子句，具體說明請(qǐng)參見CREATE TABLE文檔
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)

 # 以下為MySQL DDL語法
index_sharding_col_name:
    col_name [(length)] [ASC | DESC] # length參數(shù)僅用于在索引表拆分鍵上創(chuàng)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系列語法用于在建表后添加GSI，該系列語法在MySQL語法上新引入了GLOBAL關(guān)鍵字，用于指定添加的索引類型為GSI。目前建表后創(chuàng)建GSI存在一定限制，關(guān)于GSI的限制與約定，詳情請(qǐng)參見如何使用全局二級(jí)索引。

關(guān)于全局二級(jí)索引定義子句詳細(xì)說明，請(qǐng)參見CREATE TABLE（DRDS模式）。

示例

下面以建立普通全局二級(jí)索引為例，介紹在建表后創(chuàng)建GSI。
# 創(chuàng)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`);
# 創(chuàng)建全局二級(jí)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“只分庫不分表，分庫的拆分方式為按照”order_id“列進(jìn)行哈希。
  • 索引表：”g_i_buyer“只分庫不分表，分庫的拆分方式為按照”buyer_id“列進(jìn)行哈希，指定覆蓋列為”order_snapshot“。
  • 索引定義子句：GLOBAL INDEX `g_i_seller` ON t_order (`seller_id`) dbpartition by hash(`seller_id`)。
通過SHOW INDEX查看索引信息，包含拆分鍵order_id上的局部索引，以及seller_id、id和order_id上的GSI，其中seller_id為索引表的拆分鍵，id和order_id為默認(rèn)的覆蓋列（主鍵和主表的拆分鍵）。
說明 關(guān)于GSI的限制與約定，詳情請(qǐng)參見如何使用全局二級(jí)索引，SHOW INDEX詳細(xì)說明，請(qǐng)參見SHOW INDEX。
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 |               |   
+---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
通過SHOW GLOBAL INDEX可以單獨(dú)查看GSI信息，詳情請(qǐng)參見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 |   
+---------------------+---------+------------+------------+-------------+----------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+
查看索引表的結(jié)構(gòu)，索引表包含主表的主鍵、分庫分表鍵、默認(rèn)的覆蓋列和自定義覆蓋列，主鍵列去除了AUTO_INCREMENT屬性，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 dbpartition by hash(`seller_id`) | 
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+