PolarDB:CREATE INDEX ( DRDS mode )

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] ...

# Specific syntax that is used to create a global secondary index. For more information, see CREATE TABLE Statement on the official website of MySQL.
global_secondary_index_option:
    [COVERING (col_name,...)]
    drds_partition_options
    [VISIBLE|INVISIBLE]

# Clauses that are used for database sharding and table sharding. For more information, see CREATE TABLE Statement on the official website of MySQL.
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)

 # The DDL syntax that is supported by MySQL databases.
index_sharding_col_name:
    col_name [(length)] [ASC | DESC] # The length parameter can be used only when you create a local secondary index based on the shard key of an index table.

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}

The following example shows how to create a global secondary index for an existing table.

# Create a table.
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`);
# Create a global secondary index.
ALTER TABLE t_order ADD UNIQUE GLOBAL INDEX `g_i_buyer` (`buyer_id`) COVERING (`order_snapshot`) dbpartition by hash(`buyer_id`);

• Base table: In the preceding example, a table named t_order is created in each database shard. The data is sharded by using the hash algorithm based on the order_id column.
• Index table: In the preceding example, an index table named g_i_buyer is created for each database shard. The index values are sharded by using the hash algorithm based on the buyer_id column. The order_snapshot column is specified as a custom covering column.
• Clause that defines the global secondary index: GLOBAL INDEX `g_i_seller` ON t_order (`seller_id`) dbpartition by hash(`seller_id`).

You can use the SHOW INDEX statement to query information about indexes of a table. In the following example, the returned information includes local secondary indexes that are created based on the order_id shard key and the global secondary indexes that are created based on the seller_id, id, and order_id columns. The shard key of the index table is seller_id. The id field is the primary key of the base table, and the order_id field is the shard key of the base table. The id and order_id columns are the default covering columns.

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 |               |   
+---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+----------+---------------+  

You can use the SHOW GLOBAL INDEX statement to query information about global secondary indexes of a table. For more information, see 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 |   
+---------------------+---------+------------+------------+-------------+----------------+------------+------------------+---------------------+--------------------+------------------+---------------------+--------------------+--------+   

You can use the following statement to query the schema of an index table. A global secondary index table contains the primary key of the base table, shard keys, default covering columns, and custom covering columns. In a global secondary index table, the primary key column is not auto-increment, and local secondary indexes are not contained.

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`) | 
+------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+