更新後觸發無效緩存

Question

我試圖編寫觸發器來使我的故事數據庫的字索引無效。然而，我似乎無法弄清楚在索引操作過程中如何停止觸發器再次觸發。我知道我需要放置一條if語句來停止更新，但我似乎無法弄清楚它應該是什麼樣子。

CREATE TRIGGER trMarkStoryForReindex BEFORE UPDATE ON Chapters 
    FOR EACH ROW BEGIN 

    -- any update to any chapter invalidates the index for the whole story 
    -- we could just periodically flush the story index, but this way is 
    -- better. 
    SET New.isIndexed = FALSE; 
    -- delete the index for that story 
    -- It will get rebuilt in at most 15 minutes 
    DELETE FROM freq WHERE storyid = NEW.StoryId; 
END; 

我基本上只想觸發器只有在觸發器的update語句中沒有設置isIndexed時才觸發。

我的數據模型看起來像這樣：

章

• ID
• isIndexed
• StoryId

頻率

• 字
• storyid

Answer 1

這裏是我的解決方案建議。我已經在SQL小提琴進行了測試，它似乎工作：

-- Database setup 
create table chapters (
    id int unsigned not null auto_increment primary key, 
    isIndexed boolean default false, 
    storyId int not null, 
    index idx_storyId(storyId) 
); 

create table freq (
    word varchar(50), 
    storyId int not null, 
    index idx_storyId(storyId) 
); 

delimiter // 
create trigger bi_chapters before update on chapters 
for each row 
begin 
    if new.isIndexed = false then 
    delete from freq where storyId = new.storyId; 
    end if; 
end // 
delimiter ; 

insert into freq(word, storyId) 
values ('one', 1), ('two', 1), ('three', 2); 

insert into chapters(isIndexed, storyId) 
values (true, 1), (true, 2); 

當你（更新chapters之前）選擇freq的值，你會得到：

select * from chapters; 

| id | isIndexed | storyId | 
|----|-----------|---------| 
| 1 |  false |  1 | 
| 2 |  true |  2 | 

select * from freq; 

| word | storyId | 
|-------|---------| 
| one |  1 | 
| two |  1 | 
| three |  2 | 

現在，做一個update到章節，從select從freq再次：

update chapters 
    set isIndexed = false 
    where storyId = 1; 
select * from freq; 

| word | storyId | 
|-------|---------| 
| three |  2 | 

我做的唯一的修改是if塊檢查新行是否更新爲false。如果我已經正確理解你的問題，這將做你所需要的。

• SQL fiddle example