如何从sql中的列中删除没有任何id的唯一约束

Question

create table frontend_employee(
employee_id int primary key,
employee_name varchar(50),
employee_role varchar(50),
employee_sarlary int default 25000,
employee_boss_id int unique,
foreign key(employee_boss_id) references frontend_boss(boss_id)
);

如您所见，我没有为该 UNIQUE 约束提供任何 ID 为了给该约束提供 ID，我应该使用另一种方法，即

create table frontend_employee(
employee_id int primary key,
employee_name varchar(50),
employee_role varchar(50),
employee_sarlary int default 25000,
employee_boss_id int,
CONSTRAINT UC_employee UNIQUE (employee_boss_id),
foreign key(employee_boss_id) references frontend_boss(boss_id)
);

我已经尝试了 Google 上提供的所有方法 但它们都需要约束的名称，但我没有为 UNIQUE 约束指定任何名称 我找不到任何方法来从该列中删除该唯一约束

网上查询：-

ALTER TABLE table_name DROP CONSTRAINT unique_constraint;

Answer 1

在您的情况下，您不能仅删除唯一约束，因为外键约束中需要它。您还必须删除外键约束。 考虑以下数据示例

create table frontend_boss(
    boss_id int unique );


create table frontend_employee(
  employee_id int primary key,
  employee_name varchar(50),
  employee_role varchar(50),
  employee_sarlary int default 25000,
  employee_boss_id int unique,
  foreign key(employee_boss_id) references frontend_boss(boss_id) );
  

 show create table frontend_employee;

 CREATE TABLE `frontend_employee` (
  `employee_id` int(11) NOT NULL,
  `employee_name` varchar(50) DEFAULT NULL,
  `employee_role` varchar(50) DEFAULT NULL,
  `employee_sarlary` int(11) DEFAULT 25000,
  `employee_boss_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`employee_id`),
  UNIQUE KEY `employee_boss_id` (`employee_boss_id`),
  CONSTRAINT `frontend_employee_ibfk_1` FOREIGN KEY (`employee_boss_id`) REFERENCES `frontend_boss` (`boss_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ;

唯一约束具有自动生成的名称 

employee_boss_id

掉落

alter table frontend_employee drop constraint employee_boss_id;

错误1553（HY000）：无法删除索引“employee_boss_id”：需要在 外键约束

删除唯一约束和外键

alter table frontend_employee drop constraint employee_boss_id, drop constraint  frontend_employee_ibfk_1;
Query OK, 0 rows affected (0.045 sec)
Records: 0  Duplicates: 0  Warnings: 0

 show create table frontend_employee;

 CREATE TABLE `frontend_employee` (
  `employee_id` int(11) NOT NULL,
  `employee_name` varchar(50) DEFAULT NULL,
  `employee_role` varchar(50) DEFAULT NULL,
  `employee_sarlary` int(11) DEFAULT 25000,
  `employee_boss_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`employee_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;