本文介紹了如何創建局部索引和全局二級索引。
注意事項
在包含全局二級索引的表中使用ALTER語法，要求MySQL為5.7及以上版本，PolarDB-X 1.0為5.4.1及以上版本。
局部索引
關于局部索引，詳情清參見CREATE INDEX Statement。
全局二級索引
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] ...
# 全局二級索引特有語法，具體說明請參見CREATE TABLE文檔
global_secondary_index_option:
[COVERING (col_name,...)]
drds_partition_options
# 分庫分表子句，具體說明請參見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參數僅用于在索引表拆分鍵上創建局部索引
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關鍵字，用于指定添加的索引類型為GSI。目前建表后創建GSI存在一定限制，關于GSI的限制與約定，詳情請參見使用全局二級索引時的注意事項。
關于全局二級索引定義子句詳細說明，請參見CREATE TABLE。
示例
下面以建立普通全局二級索引為例，介紹在建表后創建GSI。
創建全局二級索引
# 創建表 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`); # 創建全局二級索引 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"列進行哈希，指定覆蓋列為"order_snapshot"。
索引定義子句：
GLOBAL INDEX `g_i_buyer` ON t_order (`buyer_id`) dbpartition by hash(`buyer_id`)。
通過
SHOW INDEX查看索引信息，包含拆分鍵order_id上的局部索引，和buyer_id、id、order_id和order_snapshot上的GSI，其中buyer_id為索引表的拆分鍵，id和order_id為默認的覆蓋列（主鍵和主表的拆分鍵），order_snapshot顯式指定的覆蓋列。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 | | +---------+------------+-----------+--------------+----------------+-----------+-------------+----------+--------+------+------------+----------+---------------+通過
SHOW GLOBAL INDEX可以單獨查看GSI信息，詳情請參見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 | 0 | g_i_buyer | buyer_id | id, order_id, order_snapshot | NULL | buyer_id | HASH | 4 | | NULL | NULL | PUBLIC | +---------------------+---------+------------+-----------+-------------+------------------------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+查看索引表的結構，索引表包含主表的主鍵、分庫分表鍵、默認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，全局唯一索引默認在索引表的所有分庫分表鍵上創建一個唯一索引，以實現全局唯一約束。
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`) | +-----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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