我有两张桌子:
// posts
+----+---------+-----------+-------------+
| id | title | content | total_votes |
+----+---------+-----------+-------------+
| 1 | title1 | content1 | 3 |
| 2 | title2 | content2 | 2 |
+----+---------+-----------+-------------+
// votes
+----+---------+-------+
| id | id_post | value |
+----+---------+-------+
| 1 | 1 | 1 |
| 2 | 1 | 1 |
| 3 | 1 | 1 |
| 4 | 2 | -1 |
| 5 | 2 | 1 |
| 6 | 2 | 1 |
| 7 | 2 | 1 |
+----+---------+-------+
现在我需要触发更新posts.total_votes
。当一个用户给出新的投票(1或-1)时,它将是votes
表中的新行,所以我想在插入votes
表后自动触发更新total_votes
表的数量{1}}并申请新的投票。有可能吗?
例如:
If new votes.values == 1 then posts.totla_votes++;
If new votes.values == -1 then posts.total_votes--;
修改
我有两个帖子表(posts_A | posts_B)。我还在投票表上添加了一个包含表名的新列。所以我需要触发更新相应的表。类似这样的事情:update new.table_name ...
而不是update posts ...
。
// posts_A
+----+---------+-----------+-------------+
| id | title | content | total_votes |
+----+---------+-----------+-------------+
| 1 | title1 | content1 | 2 |
| 2 | title2 | content2 | -1 |
+----+---------+-----------+-------------+
// posts_B
+----+---------+-----------+-------------+
| id | title | content | total_votes |
+----+---------+-----------+-------------+
| 1 | title1 | content1 | 1 |
| 2 | title2 | content2 | 3 |
+----+---------+-----------+-------------+
// votes
+----+---------+-------+------------+
| id | id_post | value | table_name |
+----+---------+-------+------------+
| 1 | 1 | 1 | post_A |
| 2 | 1 | 1 | post_A |
| 3 | 1 | 1 | post_B |
| 4 | 2 | -1 | post_A |
| 5 | 2 | 1 | post_B |
| 6 | 2 | 1 | post_B |
| 7 | 2 | 1 | post_B |
+----+---------+-------+------------+
这是我的尝试,但我不知道为什么它不起作用? :
delimiter //
create trigger total_votes_count_upd after update on votes
for each row
begin
if (new.value == 1) then
update new.table_name set total_votes = total_votes+1
where id = new.id_post;
elseif (new.value == -1) then
update new.table_name set total_votes = total_votes-1
where id = new.id_post;
end if;
end;//
delimiter //
实际上我直接替换new.table_name
而不是表(posts
)的名称。但正如我所说,它不起作用。我该如何解决?
答案 0 :(得分:2)
是的,您需要为此
创建after insert trigger
delimiter //
create trigger total_votes_count after insert on votes
for each row
begin
if (new.value == 1) then
update posts set total_votes = total_votes+1
where id = new.id_post;
elseif (new.value == -1) then
update posts set total_votes = total_votes-1
where id = new.id_post;
end if;
end;//
delimiter //
为了处理更新,所有内容保持不变,只需要另一个触发器
delimiter //
create trigger total_votes_count_upd after update on votes
for each row
begin
if (new.value == 1) then
update posts set total_votes = total_votes+1
where id = new.id_post;
elseif (new.value == -1) then
update posts set total_votes = total_votes-1
where id = new.id_post;
end if;
end;//
delimiter //
由于你有2个帖子表,你需要在if条件
中使用它delimiter //
create trigger total_votes_count after insert on votes
for each row
begin
if (new.value == 1) then
if (new.table_name == 'post_A') then
update posts_A set total_votes = total_votes+1
where id = new.id_post;
else
update posts_B set total_votes = total_votes+1
where id = new.id_post;
end if;
elseif (new.value == -1) then
if (new.table_name == 'post_A') then
update posts_A set total_votes = total_votes-1
where id = new.id_post;
else
update posts_B set total_votes = total_votes-1
where id = new.id_post;
end if ;
end if;
end;//
delimiter //
对更新触发器执行相同的操作。