MySQL触发器删除旧记录并插入新记录

Question

i have a table as below

Table name: sda_user_eform_data

ack_no   Name       Description
1        name1     This is name1
2        name2     This is name2
3        name3     This is name3

i have another table sda_user_eform_data_bckup which has exactly the same structure as sda_user_eform_data. I want to store only 5 rows(latest rows) in the sda_user_eform_data and whenever the ackno is greater than 5 the old values should be moved to the second(sda_user_eform_data_bckup) table.

For this first i have copied all the rows from sda_user_eform_data table to the sda_user_eform_data_bckup table. then i have created the following trigger where the i have checked the ack_no and if its greater than 5 then its deleted the oldest ack_no and insert the new value to the bckup table.

DELIMITER $$
create
  trigger 'copy_eform_data' AFTER INSERT
  on asdb.sda_user_eform_data
  for each row begin
  if (select count(s.ack_no) from asdb.sda_user_eform_data s)>5 then
    delete from asdb.sda_user_eform_data where old.ack_no=(select min(s.ack_no) from asdb.sda_user_eform_data s);
  insert into asdb.sda_user_eform_data_bckup select * from asdb.sda_user_eform_data where ack_no=select max(s.ack_no) from asdb.sda_user_eform_data s;
end$$
DELIMITER ;

I am not able to find out where the trigger went wrong as its not executing. Any suggestion is highly welcoming.

Thanks in advance.

Answer 1

That's most likely because your trigger doesn't even exist. The problem is here

create
  trigger 'copy_eform_data'

With the single quotes copy_eform_data is a string.

Have a look at this post: When to use single quotes, double quotes, and backticks?

Also you should read up about the NEW and OLD keywords in triggers. Your trigger probably never matches a line.

And here

where ack_no=select max(s.ack_no) from asdb.sda_user_eform_data s

you're missing parantheses.

Apart from all that, I didn't really have a deep thought about your logic to be honest, because I don't see a point in your whole question. Why would you want to have duplicate data? I guess out of performance reasons? Have your table indexed appropriately and there should be no problem. And to get the 5 latest entries of your table simply use

FROM yourTable
ORDER BY when_was_the_entry_created_or_something DESC 
LIMIT 5

You can have columns like

created timestamp DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP

to use in your ORDER BY . And you probably want an index on that column.

Answer 2

I doing some changes in your query. Revert back if it helps.

DELIMITER $$
create
  trigger 'copy_eform_data' AFTER INSERT
  on asdb.sda_user_eform_data
  for each row begin
  insert into asdb.sda_user_eform_data_bckup 
   select * from asdb.sda_user_eform_data ORDER BY ack_no DESC LIMIT 1
  if (select count(s.ack_no) from asdb.sda_user_eform_data s)>=5 then
    delete from asdb.sda_user_eform_data;  
end$$
DELIMITER ;

But make sure that when you are entering records into "asdb.sda_user_eform_data" after clearing table, "ack_no" should again start from 1

Answer 3

I was searching for a solution to create trigger for deleting records and came across your forum. However, I know this is over a year post and you've most likely solved the issue, but I would like to try to answer your post. I think you need a "End If" before your end $$.

So it would be:

 DELIMITER $$
create
 trigger 'copy_eform_data' AFTER INSERT
 on asdb.sda_user_eform_data
 for each row begin
 if (select count(s.ack_no) from asdb.sda_user_eform_data s)>5 then
 delete from asdb.sda_user_eform_data where old.ack_no=(select min(s.ack_no) from  asdb.sda_user_eform_data s);
 insert into asdb.sda_user_eform_data_bckup select * from asdb.sda_user_eform_data where ack_no=select max(s.ack_no) from asdb.sda_user_eform_data s;
END IF;
end$$
DELIMITER ;