MySQL触发器从数据库中选择并更新列

Question

I have this trigger. If the incoming log agrees with input filter, than is not saved into database. But, I want to keep number of "hits" of each Primitive_filter. I have a column named hit_rate, which is int(30). Is there some way how to do that? Maybe specific error? Or sth else? Thx for help.

UPDATE Primitive_filters SET hit_rate = hit_rate + 1 where Primitive_filters.id = ???;

trigger

delimiter //
CREATE TRIGGER inputFilter
before insert
on Logs
for each row
begin
declare msg varchar(255);
IF (SELECT COUNT(*) FROM Primitive_filters, Primitive_in_filter, Filters WHERE 
Filters.name = "input" AND Filters.id = Primitive_in_filter.id_filter AND Primitive_in_filter.id_primitive = Primitive_filters.id AND
(Primitive_filters.id_host LIKE CONCAT('%',(SELECT host FROM Hosts WHERE id = new.id_host),'%') OR Primitive_filters.id_host IS NULL) AND
(Primitive_filters.facility LIKE CONCAT('%',new.facility,'%') OR Primitive_filters.facility IS NULL) AND
(Primitive_filters.priority LIKE CONCAT('%',new.priority,'%') OR Primitive_filters.priority IS NULL) AND
(Primitive_filters.program LIKE CONCAT('%',new.program,'%') OR Primitive_filters.program IS NULL) AND
(new.msg REGEXP Primitive_filters.msg OR Primitive_filters.msg IS NULL)) > 0 THEN CALL raise_error; END IF; 
END //

delimiter ;

Answer 1

This is NOT the answer to your question.

It's only a hint how to fix a potentially serious performance problem in your code.

Don't use this:

IF (SELECT COUNT(*) FROM ... giant query ...) > 0 
THEN CALL raise_error; 
END IF; 

Use this instead:

IF EXISTS (SELECT 1 FROM ... giant query ...)
THEN CALL raise_error; 
END IF; 

The former condition calculates a count ... it must read all rows returned by the query
If the query returns billion rows, it must reads them all --> because you asked give me a count of rows .
Then, after the query return the count, there is a check: if the query returns at least one row , then do something.

The latter condition stops executing the query when the query returns first row, saving time and resources.