sql query between 3 tables and an input value

SELECT `identifier`
FROM `sys_file`
JOIN `sys_file_reference`
ON sys_file.uid = sys_file_reference.uid_local
JOIN `tx_news_domain_model_news`
ON sys_file_reference.uid_foreign = tx_news_domain_model_news.uid
WHERE sys_file_reference.pid = "13"
AND tx_news_domain_model_news.title = "the GPvar of my input title form..."