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ADD INDEX

ALTER TABLE.. ADD INDEX 语句用于在已有表中添加一个索引。在 TiDB 中，ADD INDEX 为在线操作，不会阻塞表中的数据读写。

语法图

AlterTableStmt:

AlterTableStmt

AlterTableSpec:

AlterTableSpec

Constraint:

Constraint

ConstraintKeywordOpt:

ConstraintKeywordOpt

ConstraintElem:

ConstraintElem

IndexNameAndTypeOpt:

IndexNameAndTypeOpt

IndexPartSpecificationList:

IndexPartSpecificationList

IndexPartSpecification:

IndexPartSpecification

IndexOptionList:

IndexOptionList

IndexOption:

IndexOption

KeyOrIndex:

KeyOrIndex

IndexKeyTypeOpt:

IndexKeyTypeOpt

IndexInvisible:

IndexInvisible

IndexTypeName:

IndexTypeName

示例

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)
INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.03 sec)
Records: 5  Duplicates: 0  Warnings: 0
EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+-------------------------+----------+-----------+---------------+--------------------------------+
| id                      | estRows  | task      | access object | operator info                  |
+-------------------------+----------+-----------+---------------+--------------------------------+
| TableReader_7           | 10.00    | root      |               | data:Selection_6               |
| └─Selection_6           | 10.00    | cop[tikv] |               | eq(test.t1.c1, 3)              |
|   └─TableFullScan_5     | 10000.00 | cop[tikv] | table:t1      | keep order:false, stats:pseudo |
+-------------------------+----------+-----------+---------------+--------------------------------+
3 rows in set (0.00 sec)
ALTER TABLE t1 ADD INDEX (c1);
Query OK, 0 rows affected (0.30 sec)
EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| id                     | estRows | task      | access object          | operator info                               |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| IndexReader_6          | 0.01    | root      |                        | index:IndexRangeScan_5                      |
| └─IndexRangeScan_5     | 0.01    | cop[tikv] | table:t1, index:c1(c1) | range:[3,3], keep order:false, stats:pseudo |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
2 rows in set (0.00 sec)

MySQL 兼容性

  • 不支持 FULLTEXT，HASH 和 SPATIAL 索引。
  • 不支持 VISIBLE/INVISIBLE 索引（目前只有 master 分支上真正支持此功能）。
  • 不支持降序索引（类似于 MySQL 5.7）。
  • 目前尚不支持在一条中同时添加多个索引。
  • 默认无法向表中添加 PRIMARY KEY，在开启 alter-primary-key 配置项后可支持此功能，详情可参考：alter-primary-key。

另请参阅

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