Question

我正在尝试从表帐户中删除一行，但其中一列是另一个表的外键。我试过跑： ALTER TABLE depositor DROP FOREIGN KEY account_number; 但它随后吐出一个错误说：

ORA-00905: missing keyword

我错过了哪个关键字？

我不知道它是否有帮助，但创建表存放者的原始声明是：

create table depositor
   (customer_name   varchar(15) not null,
    account_number  varchar(15) not null,
    primary key(customer_name, account_number),
    foreign key(account_number) references account(account_number),
    foreign key(customer_name) references customer(customer_name));


  create table customer
       (customer_name   varchar(15) not null,
        customer_street     varchar(12) not null,
        customer_city   varchar(15) not null,
        primary key(customer_name));

create table account
   (account_number  varchar(15) not null,
    branch_name     varchar(15) not null,
    balance         number not null,
    primary key(account_number));

实际表中插入了这些表：

insert into customer values ('Jones', 'Main', 'Harrison');
insert into customer values ('Smith', 'Main', 'Rye');
insert into customer values ('Hayes', 'Main', 'Harrison');
insert into customer values ('Curry', 'North', 'Rye');
insert into customer values ('Lindsay', 'Park', 'Pittsfield');
insert into customer values ('Turner', 'Putnam', 'Stamford');
insert into customer values ('Williams', 'Nassau', 'Princeton');
insert into customer values ('Adams', 'Spring', 'Pittsfield');
insert into customer values ('Johnson', 'Alma', 'Palo Alto');
insert into customer values ('Glenn', 'Sand Hill', 'Woodside');
insert into customer values ('Brooks', 'Senator', 'Brooklyn');
insert into customer values ('Green', 'Walnut', 'Stamford');
insert into customer values ('Jackson', 'University', 'Salt Lake');
insert into customer values ('Majeris', 'First', 'Rye');
insert into customer values ('McBride', 'Safety', 'Rye');
insert into customer values ('Jones', 'Second', 'Bennington');

insert into account values ('A-101', 'Downtown', 500);
insert into account values ('A-215', 'Mianus', 1000);
insert into account values ('A-102', 'Perryridge', 400);
insert into account values ('A-305', 'Round Hill', 350);
insert into account values ('A-201', 'Perryridge', 900);
insert into account values ('A-222', 'Redwood', 100000);
insert into account values ('A-217', 'Brighton', 7500);
insert into account values ('A-333', 'Central', 8500);
insert into account values ('A-444', 'North Town', 6250);

insert into depositor values ('Johnson','A-101');
insert into depositor values ('Smith', 'A-215');
insert into depositor values ('Hayes', 'A-102');
insert into depositor values ('Hayes', 'A-101');
insert into depositor values ('Turner', 'A-305');
insert into depositor values ('Johnson','A-201');
insert into depositor values ('Jones', 'A-217');
insert into depositor values ('Lindsay', 'A-222');
insert into depositor values ('Majeris', 'A-333');
insert into depositor values ('Smith', 'A-444');
insert into depositor values ('Johnson','A-444');

Answer 1

这是因为您在创建表时没有命名CONSTRAINT，因此它是自动生成的。

做一个：

SHOW CREATE TABLE depositor;

它将显示如下内容：

CREATE TABLE `depositor` (
  `customer_name` varchar(15) NOT NULL,
  `account_number` varchar(15) NOT NULL,
  PRIMARY KEY (`customer_name`,`account_number`),
  KEY `account_number` (`account_number`),
  CONSTRAINT `depositor_ibfk_1` FOREIGN KEY (`account_number`) REFERENCES `account` (`account_number`),
  CONSTRAINT `depositor_ibfk_2` FOREIGN KEY (`customer_name`) REFERENCES `customer` (`customer_name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |

其中depositor_ibfk_1是您可以使用命令删除的约束名称：

ALTER TABLE depositor DROP FOREIGN KEY depositor_ibfk_1;

Answer 2

在mysql中创建外键时需要命名约束：

首先在alter table中添加约束 -

ALTER TABLE depositor ADD CONSTRAINT fk_account_number FOREIGN KEY ('account_number') REFERENCES 'account'('account_number') ON UPDATE RESTRICT ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED;

然后，使用您编写的sql将fkey放入存款表

ALTER TABLE depositor DROP FOREIGN KEY fkey_account_number;

为什么我不能从表中删除这个外键？

2 个答案: