CREATE INDEX

CREATE INDEX 语句用于在已有表中添加新索引,功能等同于 ALTER TABLE .. ADD INDEX。包含该语句提供了 MySQL 兼容性。

语法图

CreateIndexStmt:

CreateIndexStmt

CreateIndexStmtUnique:

CreateIndexStmtUnique

Identifier:

Identifier

IndexTypeOpt:

IndexTypeOpt

TableName:

TableName

IndexColNameList:

IndexColNameList

IndexOptionList:

IndexOptionList

IndexOption:

IndexOption

示例

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.10 sec)
INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 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)
CREATE INDEX c1 ON t1 (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)
ALTER TABLE t1 DROP INDEX c1;
Query OK, 0 rows affected (0.30 sec)
CREATE UNIQUE INDEX c1 ON t1 (c1);
Query OK, 0 rows affected (0.31 sec)

相关系统变量

CREATE INDEX 语句相关的系统变量有 tidb_ddl_reorg_worker_cnttidb_ddl_reorg_batch_sizetidb_ddl_reorg_priority,具体可以参考TiDB 特定系统变量

MySQL 兼容性

  • 不支持 FULLTEXTHASHSPATIAL 索引。
  • 不支持降序索引 (类似于 MySQL 5.7)。
  • 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

另请参阅

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