傳遞標量查詢結果以合併

Question

如何將標量[單行，單值]查詢的結果傳遞到合併？我想挑優先級（最大優先級表至今）+ 1，[0，如果它是第一行。]

create trigger priority_SuperRuleSamples before insert on SuperRuleSamples 
FOR EACH ROW 
    SET NEW.Priority=coalesce(NEW.Priority, 
    coalesce(
    select Priority from SuperRuleSamples order by Priority desc limit 1, 
    -1 
    )+1 
) 

Answer 1

似乎有在查詢括號問題。你可以試試這個嗎？

 

create trigger priority_SuperRuleSamples before insert on SuperRuleSamples 
FOR EACH ROW 
    SET NEW.Priority=coalesce(NEW.Priority, 
    coalesce(
    (select Priority from SuperRuleSamples order by Priority desc limit 1), 
    -1 
    )+1 
)