50 lines
2.6 KiB
Markdown
50 lines
2.6 KiB
Markdown
创建索引
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=========================
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本节主要介绍如何通过 `CREATE INDEX` 语句在非分区表上创建索引，分区表上索引的创建请参见 [局部索引](../../../6.administrator-guide/5.data-distribution-and-link-management/1.partition-table-and-partitioned-index-management/6.create-an-index-on-a-partition-table/1.local-index.md)章节。
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OceanBase 数据库支持在非分区表和分区表上创建索引，索引可以是局部索引或全局索引，也可以是唯一索引或普通索引。如果是分区表的唯一索引，则唯一索引必须包含表分区的拆分键。
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MySQL 模式下，创建索引的 SQL 语法格式如下：
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```sql
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CREATE [UNIQUE] INDEX index_name ON table_name ( column_list ) [LOCAL | GLOBAL] [ PARTITION BY column_list PARTITIONS N ] ;
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```
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MySQL 租户里，索引名称在表范围内不能重复，查看索引可以通过命令 `SHOW INDEX`。
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在 MySQL 租户里，新增索引还有一种方法，其 SQL 语法格式如下：
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```sql
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ALTER TABLE table_name
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ADD INDEX|KEY index_name ( column_list ) ;
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```
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该语句可以一次增加多个索引，索引关键字用 `INDEX` 或 `KEY` 都可以。
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示例：为非分区表创建普通索引。
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```sql
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obclient> CREATE TABLE test (c1 int primary key, c2 VARCHAR(10));
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Query OK, 0 rows affected (0.20 sec)
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obclient> CREATE INDEX idx ON test (c1, c2);
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Query OK, 0 rows affected (0.59 sec)
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obclient> SHOW INDEX FROM test;
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
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| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible |
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
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| test | 0 | PRIMARY | 1 | c1 | A | NULL | NULL | NULL | | BTREE | available | | YES |
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| test | 1 | idx | 1 | c1 | A | NULL | NULL | NULL | | BTREE | available | | YES |
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| test | 1 | idx | 2 | c2 | A | NULL | NULL | NULL | YES | BTREE | available | | YES |
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+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
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3 rows in set (0.00 sec)
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```
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