Question

我尝试做的是我的数据库中的INSERT个订阅者，但是IF EXISTS它应该UPDATE行，ELSE INSERT INTO一个新行。

当然，我首先连接到数据库，然后从网址字符串GET，$name，$email和$birthday连接到数据库。

$con=mysqli_connect("localhost","---","---","---");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$name=$_GET['name']; 
$email=$_GET['email'];
$birthday=$_GET['birthday'];

这样可行，但只需添加新行;

mysqli_query($con,"INSERT INTO subs (subs_name, subs_email, subs_birthday)
VALUES ('$name', '$email', '$birthday')");

mysqli_close($con);

这是我尝试的内容;

mysqli_query($con,"INSERT INTO subs (subs_name, subs_email, subs_birthday)
VALUES '$name', '$email', '$birthday'
ON DUPLICATE KEY UPDATE subs_name = VALUES($name), subs_birthday = VALUES($birthday)");
mysqli_close($con);

和

mysqli_query($con,"IF EXISTS (SELECT * FROM subs WHERE subs_email='$email')
    UPDATE subs SET subs_name='$name', subs_birthday='$birthday' WHERE subs_email='$email'
ELSE
    INSERT INTO subs (subs_name, subs_email, subs_birthday) VALUES ('$name', '$email', '$birthday')");
mysqli_close($con);

和

mysqli_query($con,"IF NOT EXISTS(SELECT * FROM subs WHERE subs_email='$email')
Begin
INSERT INTO subs (subs_name, subs_email, subs_birthday)
VALUES ('$name', '$email', '$birthday')
End");
mysqli_close($con);

但它们都不起作用，我做错了什么？

非常感谢任何帮助！

Answer 1

在subs_email列上创建UNIQUE constraint，如果尚不存在：
```
ALTER TABLE subs ADD UNIQUE (subs_email)
```

使用INSERT ... ON DUPLICATE KEY UPDATE：

INSERT INTO subs
  (subs_name, subs_email, subs_birthday)
VALUES
  (?, ?, ?)
ON DUPLICATE KEY UPDATE
  subs_name     = VALUES(subs_name),
  subs_birthday = VALUES(subs_birthday)

您可以使用UPDATE子句中的VALUES（col_name）函数引用INSERT ... ON的INSERT部分的列值 DUPLICATE KEY UPDATE - dev.mysql.com

请注意，我在字符串文字的位置使用了参数占位符，因为一个真的应该使用参数化语句defend against SQL injection attacks。

Answer 2

尝试一下：

INSERT INTO `center_course_fee` (`fk_course_id`,`fk_center_code`,`course_fee`) VALUES ('69', '4920153', '6000') ON DUPLICATE KEY UPDATE `course_fee` = '6000';

SQL - IF EXISTS UPDATE ELSE INSERT INTO

2 个答案: