Perl Mysql DBD :: mysql :: st执行失败

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;

我收到这个错误

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` FOREIGN KEY(`ITEMS_TO`)REFERENCES`users`(`USERID `))

当我运行这个:

$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();

它没有ITEMS_FROM,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

你不应该NULL引用引号.那是试图设置ITEMS_TO为文字字符串'NULL',而不是空值.MySQL然后会尝试将其转换为BIGINT; 因为它看起来不像是一个数字,它将被转换为0.由于没有user_id = 0在users表中,外键检查失败.

您应该使用Perl值undef来表示SQL null值:

$NULL = undef;

看哪哪个代表null？undef或空字符串