无法删除索引

Question

以下创建语句显示了我的一个 MariaDB 表的当前结构。

CREATE TABLE `councilor` (
    `id` BIGINT(20) NOT NULL AUTO_INCREMENT,
    `user` BIGINT(20) NOT NULL,
    `council` INT(11) NOT NULL,
    `role` CHAR(50) NOT NULL DEFAULT 'member' COLLATE 'utf8_persian_ci',
    `cDate` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
    `uDate` TIMESTAMP NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
    `startDate` DATETIME NULL DEFAULT NULL,
    `endDate` DATETIME NULL DEFAULT NULL,
    `responsibility` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8_persian_ci',
    `details` TEXT NULL COLLATE 'utf8_persian_ci',
    PRIMARY KEY (`id`),
    UNIQUE INDEX `userId_councilId` (`user`, `council`),
    INDEX `council_user_council_foreign` (`council`)
)
COLLATE='utf8_persian_ci'
ENGINE=InnoDB
ROW_FORMAT=COMPACT
AUTO_INCREMENT=11;

我需要删除唯一索引，但是尝试删除两个键中的任何一个都会失败。

ALTER TABLE `councilor`
    DROP INDEX `userId_councilId`;

/* SQL 错误 (1553): 无法删除索引 'userId_councilId': 在外键约束中需要 */

ALTER TABLE `councilor`
    DROP INDEX `council_user_council_foreign`;

/* SQL 错误 (1553): 无法删除索引 'council_user_council_foreign': 在外键约束中需要 */

删除所有表的行也无济于事。但是，如果上述脚本创建了一个新表，则不会出现此问题。

Answer 1

你必须先删除外键约束，然后

ALTER TABLE mytable DROP FOREIGN KEY [Foreign_key_constraint_name];

然后你可以删除索引

Answer 2

18:18:46 ALTER TABLE location DROP INDEX unique_name_to_supplier 错误 代码：1553。无法删除索引“unique_name_to_supplier”：需要在 外键约束 0.063 秒

这意味着您正在尝试删除用于 FK 的索引。

MySQL 需要外键和引用键的索引，以便 外键检查可以很快并且不需要表扫描。在里面 引用表，必须有外键所在的索引 列按相同顺序列为第一列。这样一个 如果没有，则在引用表上自动创建索引 存在。如果您创建，此索引可能会在稍后被静默删除 另一个可用于强制外键约束的索引。 index_name，如果给定，则如前所述使用。

http://dev.mysql.com/doc/refman/5.7/en/create-table-foreign-keys.html

所以你需要修复：

1.摆脱FK

2.删除索引本身

3.再次创建FK

命令如下：

#removing FK
    ALTER TABLE `location`  DROP FOREIGN KEY `FK_SUPPLIER`;

#droping unique Index
    ALTER TABLE `location`  DROP INDEX `unique_name_to_supplier` ;

#creating new FK with proper Index    
    ALTER TABLE `location` 
    ADD INDEX `FK_SUPPLIER_idx` (`supplier_id` ASC);
    ALTER TABLE `location` 
    ADD CONSTRAINT `FK_SUPPLIER`
      FOREIGN KEY (`supplier_id`)
      REFERENCES `supplier` (`id`)
      ON DELETE NO ACTION
      ON UPDATE NO ACTION;

完整的 sql 日志：

mysql>
mysql> CREATE TABLE supplier (
    ->  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.38 sec)

mysql> CREATE TABLE location (
    ->  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
    ->  name VARCHAR(10) NOT NULL,
    ->  supplier_id INT UNSIGNED NOT NULL
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.32 sec)

mysql> ALTER TABLE location ADD CONSTRAINT FK_SUPPLIER FOREIGN KEY FK_SUPPLIER (supplier_id)
    ->    REFERENCES supplier (id) ON DELETE RESTRICT ON UPDATE RESTRICT;
Query OK, 0 rows affected (0.41 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE location ADD UNIQUE INDEX unique_name_to_supplier (supplier_id,name);
Query OK, 0 rows affected (0.24 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table location;
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table
                                                                                                                                |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| location | CREATE TABLE `location` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(10) NOT NULL,
  `supplier_id` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `unique_name_to_supplier` (`supplier_id`,`name`),
  CONSTRAINT `FK_SUPPLIER` FOREIGN KEY (`supplier_id`) REFERENCES `supplier` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

mysql>
mysql>
mysql>
mysql> ALTER TABLE `location`  DROP FOREIGN KEY `FK_SUPPLIER`;
Query OK, 0 rows affected (0.17 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> ALTER TABLE `location`  DROP INDEX `unique_name_to_supplier` ;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> ALTER TABLE `location`
    -> ADD INDEX `FK_SUPPLIER_idx` (`supplier_id` ASC);
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE `location`
    -> ADD CONSTRAINT `FK_SUPPLIER`
    ->   FOREIGN KEY (`supplier_id`)
    ->   REFERENCES `supplier` (`id`)
    ->   ON DELETE NO ACTION
    ->   ON UPDATE NO ACTION;
Query OK, 0 rows affected (0.68 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table location
    -> ;
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table    | Create Table
                                                                                                                                                  |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| location | CREATE TABLE `location` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(10) NOT NULL,
  `supplier_id` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  KEY `FK_SUPPLIER_idx` (`supplier_id`),
  CONSTRAINT `FK_SUPPLIER` FOREIGN KEY (`supplier_id`) REFERENCES `supplier` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Answer 3

您必须先删除 FOREIGN KEY 约束，然后删除索引并重新创建 FOREIGN 键。