php - hp insert into语句出错

Question

$db->query_unbuffered("insert into pd_file2tag set tag_name=1,file_id=($file_str)");

sql执行结果

[PHPDisk error!] insert into pd_file2tag set tag_name=1,file_id=('13','12','11','10','9','8','7','5','4','3','2','1')

MySQL Info: Operand should contain 1 column(s) , 1241

请问是哪里出错了呢