mysql - 在以下程序中，触发器的IF语法是什么意思？

DELIMITER $$
create trigger mytable_check before insert on test.mytable for each row
begin
 if new.id_category in ('list','of','special','categories')
    and exists
      (select * from mytable
       where id_category=new.id_category
         and keywords=new.keywords) then
    call fail(concat('id_category,keywords must be unique when id_category is: ',new.id_category));
 end if;
end $$
DELIMITER ;

我在理解此触发语句时遇到了一些小问题。你能给我解释一下这句话吗？

if new.id_category in ('list','of','special','categories')

声明的意思是？

最佳答案

new.id_category = 'list'
or
new.id_category = 'of'
or
new.id_category = 'special'
or
new.id_category = 'categories'