我正在向表中添加组合索引，但该索引会删除已存在的索引（请参阅fk_service_catalog_parameter_component如何消失）。知道为什么吗？
mysql> show indexes from service_catalog_parameter;
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| service_catalog_parameter | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_resource | 1 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_component | 1 | component_id | A | 0 | NULL | NULL | YES | BTREE | | |
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)
mysql> ALTER TABLE `service_catalog_parameter` ADD UNIQUE INDEX `resource_parameter_component_unique` (`component_id`, `resource_id`, `parameter_name`);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show indexes from service_catalog_parameter;
+---------------------------+------------+---------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------------------+------------+---------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| service_catalog_parameter | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 1 | component_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 2 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 3 | parameter_name | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_resource | 1 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
+---------------------------+------------+---------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
5 rows in set (0.00 sec)
mysql>
当我更改索引中列的顺序时，我的脑袋完全爆炸。
mysql> show indexes from service_catalog_parameter;
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| service_catalog_parameter | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_resource | 1 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_component | 1 | component_id | A | 0 | NULL | NULL | YES | BTREE | | |
+---------------------------+------------+----------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.01 sec)
mysql> ALTER TABLE `service_catalog_parameter` ADD UNIQUE INDEX `resource_parameter_component_unique` (`parameter_name`, `component_id`, `resource_id`);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show indexes from service_catalog_parameter;
+---------------------------+------------+----------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------------------+------------+----------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| service_catalog_parameter | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 1 | parameter_name | A | 0 | NULL | NULL | | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 2 | component_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 0 | resource_parameter_component_unique | 3 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_resource | 1 | resource_id | A | 0 | NULL | NULL | YES | BTREE | | |
| service_catalog_parameter | 1 | fk_service_catalog_parameter_component | 1 | component_id | A | 0 | NULL | NULL | YES | BTREE | | |
+---------------------------+------------+----------------------------------------+--------------+----------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
6 rows in set (0.00 sec)
mysql>