Question

CREATE TABLE users(

  USERID BIGINT AUTO_INCREMENT,
  FNAME  CHAR(50),                        
  LNAME  CHAR(50), 
  EMAIL  CHAR (100),               
  PHONE  CHAR (50),        
  PRIMARY KEY (USER_ID),
  UNIQUE KEY EMAIL (EMAIL),
  UNIQUE KEY PHONE (PHONE)
) ENGINE=InnoDB CHARSET=utf8mb4;


CREATE TABLE items(
  ITEMS_ID       BIGINT AUTO_INCREMENT,                       
  USERID         BIGINT,    
  ITEMS_TO       BIGINT,
  ITEMS_FROM     BIGINT,                     
  ACCEPTED_ITEMS BIGINT,                     
  PRIMARY KEY (ITEMS_ID),
  FOREIGN KEY (USERID) REFERENCES users(USERID),
  FOREIGN KEY (ITEMS_TO) REFERENCES users(USERID),
  FOREIGN KEY (ITEMS_FROM) REFERENCES users(USERID),
  FOREIGN KEY (ACCEPTED_ITEMS) REFERENCES users(USERID)
) ENGINE=InnoDB CHARSET=utf8mb4;

我收到此错误

DBD :: mysql :: st执行失败：无法添加或更新子行：外键约束失败（“ db701”。`items`，CONSTRAINT `items_ibfk_2`外键（`ITEMS_TO`）参考`users`（`USERID`））

运行此命令时

$ID = '1';
$NULL = 'NULL';
$ID2 = '2';
$ID3 = '1';

my $update = $DBH->prepare("UPDATE items SET ITEMS_TO =?, ITEMS_FROM =? WHERE USERID =? AND ITEMS_ID = ?");
$update->execute($ID, $NULL, $ID2, $ID3);
$update->finish();

它在没有ITEMS_FROM的情况下可以工作，我想将ITEMS_FROM设置为null。

这有效：

my $update = $DBH->prepare("UPDATE items SET ITEMS_TO =? WHERE USERID =? AND ITEMS_ID = ?");
$update->execute($ID, $ID2, $ID3);
$update->finish();

Answer 1

您不应该在引号中加上NULL。试图将ITEMS_TO设置为文字字符串'NULL'，而不是空值。然后，MySQL将尝试将其转换为BIGINT；由于它看起来不像数字，它将被转换为0。由于user_id = 0表中没有users，因此外键检查失败。

您应该使用Perl值undef来表示SQL空值：

$NULL = undef;

请参见Which one represents null? undef or empty string

Perl Mysql DBD :: mysql :: st执行失败

1 个答案: