Question

以下create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'：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'：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新表，则不会发生此问题。

Answer 1

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'：a中需要外键约束0.063秒

这意味着您正在尝试删除用于FK的索引。

MySQL要求外键和引用键上的索引外键检查可以很快，不需要表扫描。在里面引用表时，必须有一个索引所在的外键列以相同顺序列为第一列。这样的如果不是，则会自动在引用表上创建索引存在。如果您创建，可能会稍后以静默方式删除此索引另一个可用于强制执行外键约束的索引。如果给定，则使用index_name，如前所述。

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

因此需要修复：

1.取消FK

2.删除索引本身

3.再次创建FK

以下是命令：

#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 2

首先必须删除FOREIGN KEY约束，然后删除索引并重新创建FOREIGN键。

Answer 3

您必须首先删除外键约束

ALTER TABLE mytable DROP FOREIGN KEY [Foreign_key_constraint_name];

并且可以删除索引

删除索引是不可能的

3 个答案: