我尝试在SQL中创建INSERT WHERE，但它给了我一个错误[重复]

When I try to insert data where with code:

$query =  dbConnect()->prepare("INSERT INTO users(key) WHERE mail='$mail' VALUES ('$key')");

I'm using XAMPP, it gives me an error:

Uncaught PDOException: SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'key) WHERE mail='maciej@localhost' VALUES (key)' at line 1 in C:\xampp\htdocs\PHP7_loginestore\index.php:38

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You should use backticks for key (because is a reserved word)
and not use where

"INSERT INTO users(`key`)  VALUES ('$key')"

or if you need an update

"UPDATE users
 set  `key` = '$key'
 where mail = '$mail'"

The guess is that you want update:

update users
    set key = '$key'
    where mail = '$mail' ;

You should also learn to use parameters for values in queries. Substituting strings into the query string introduces the possibility of unexpected errors and makes the code vulnerable to SQL injection attacks.