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:
AlterTableSpec:
ColumnKeywordOpt:
ColumnDef:
ColumnPosition:
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 | count | task | operator info |
+---------------------+----------+------+-------------------------------------------------------------+
| TableReader_7 | 10.00 | root | data:Selection_6 |
| └─Selection_6 | 10.00 | cop | eq(test.t1.c1, 3) |
| └─TableScan_5 | 10000.00 | cop | table:t1, range:[-inf,+inf], 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 | count | task | operator info |
+-------------------+-------+------+-----------------------------------------------------------------+
| IndexReader_6 | 10.00 | root | index:IndexScan_5 |
| └─IndexScan_5 | 10.00 | cop | table:t1, index: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。 - 不支持降序索引(类似于 MySQL 5.7)。
- 目前尚不支持同时添加多个索引。
- 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,详情参考:alter-primary-key。