KEY is a Reserved Word. As documented under Schema Object Names:
If an identifier contains special characters or is a reserved word, you must quote it whenever you refer to it. (Exception: A reserved word that follows a period in a qualified name must be an identifier, so it need not be quoted.)
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The identifier quote character is the backtick (“`”):
mysql> SELECT * FROM `select` WHERE `select`.id > 100;
If the ANSI_QUOTES SQL mode is enabled, it is also permissible to quote identifiers within double quotation marks:
mysql> CREATE TABLE "test" (col INT);
ERROR 1064: You have an error in your SQL syntax...
mysql> SET sql_mode='ANSI_QUOTES';
mysql> CREATE TABLE "test" (col INT);
Query OK, 0 rows affected (0.00 sec)
Therefore:
mysql_query("INSERT INTO `keys` (username, `key`, vreme) VALUES ('$user', '$acckey', '$keyexp') ")
