如何使用触发器检查复合列上的INSERT操作？

Question

我有下一个表：教师，教师，主题和科目。每个教师都有一个主题列表

我想使用checkthe faculty_subjects表格 - 每个教师不应该多次拥有相同的主题。因此，faculty_subjects表格中的每条记录都有一对唯一的Faculty_idFaculty - Subject_idSubject。

我正在尝试添加下面列出的触发器：

DELIMITER $$
CREATE TRIGGER `Faculty_Subjects_BINS` BEFORE INSERT ON `Faculty_Subjects` FOR EACH ROW
BEGIN
    -- throw exception when condition not satisfied
    IF ( (NEW.`Subject_idSubject`= `Subject_idSubject`) AND (NEW.`Faculty_idFaculty`= `Faculty_idFaculty`)) THEN
        SIGNAL SQLSTATE '45000'
            SET MESSAGE_TEXT = 'This faculty already add this subject as preliminary', MYSQL_ERRNO = 1001;
    END IF;
END;

但我收到错误1109或1054。如何实现这一功能？

我正在使用MySQL数据库。