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:

CreateIndexStmtUnique:

Identifier:

IndexTypeOpt:

TableName:

IndexColNameList:

IndexOptionList:

IndexOption:

示例

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, c1 INT NOT NULL);
Query OK, 0 rows affected (0.10 sec)
mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0
mysql> 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 |
+---------------------+----------+------+-------------------------------------------------------------+
 rows in set (0.00 sec)
mysql> CREATE INDEX c1 ON t1 (c1);
Query OK, 0 rows affected (0.30 sec)
mysql> 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 |
+-------------------+-------+------+-----------------------------------------------------------------+
 rows in set (0.00 sec)
mysql> ALTER TABLE t1 DROP INDEX c1;
Query OK, 0 rows affected (0.30 sec)
mysql> CREATE UNIQUE INDEX c1 ON t1 (c1);
Query OK, 0 rows affected (0.31 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）。
• 无法向表中添加 PRIMARY KEY。

另请参阅

• ADD INDEX
• DROP INDEX
• RENAME INDEX
• ADD COLUMN
• CREATE TABLE
• EXPLAIN