MySQL trigger On Insert/Update events

问题

So I have two tables like this...

ext_words
-------------
| id | word |
-------------
| 1  | this |
-------------
| 2  | that |
-------------
| 3  | this |
-------------

ext_words_count
---------------------
| id | word | count |
---------------------
| 1  | this |   2   |
---------------------
| 2  | that |   1   |
---------------------

I am trying to create a trigger that will:

update ext_words_count.count when ext_words.word is updated.

To further complicate matters,

if ext_words.word does not exist in ext_words_count when ext_words is updated, I would like to insert it into ext_words_count and set count as 1.

I have been looking at similar questions:
1. Before / after insert trigger using auto increment field, and
2. Using Trigger to update table in another database
trying to combine the 2. Here is what I have so far:

DELIMITER $$
CREATE TRIGGER update_count
AFTER UPDATE ON ext_words
FOR EACH ROW
BEGIN

  UPDATE ext_words_count
    SET word_count = word_count + 1
  WHERE word = NEW.word;

END;
$$
DELIMITER ;

Any advice and direction is greatly appreciated. Or possibly another method that I have overlooked and as always thanks in advance!

UPDATE:
I have opted for using 2 triggers, one for INSERT and one for UPDATE because I am not that familiar with conditional statements in MySQL.

DELIMITER $$
CREATE TRIGGER insert_word AFTER INSERT ON ext_words
  FOR EACH ROW
    BEGIN
      INSERT IGNORE INTO ext_words_count (word) VALUES (NEW.word);
    END;
$$
DELIMITER ;

and

DELIMITER $$
CREATE TRIGGER update_word AFTER UPDATE ON ext_words
  FOR EACH ROW
    BEGIN
      UPDATE ext_words_count 
      SET word_count = word_count + 1 
      WHERE word = NEW.word;
    END;
$$
DELIMITER ;

The INSERT query is working great, however the UPDATE query is not updating word_count. Is there something I missed in the update query..?

回答1:

With Grijesh's perfect help and his suggestion to use conditional statements, I was able to get ONE trigger that does both tasks. Thanks again Grijesh

 DELIMITER $$ 
 CREATE TRIGGER update_count AFTER INSERT ON ext_words 
 FOR EACH ROW 
   BEGIN
     IF NOT EXISTS (SELECT 1 FROM ext_words_count WHERE word = NEW.word) THEN
       INSERT INTO ext_words_count (word) VALUES (NEW.word);
   ELSE
       UPDATE ext_words_count SET word_count = word_count + 1 WHERE word = NEW.word;
   END IF;
  END $$    
 DELIMITER;

回答2:

avoid use of keywords like count as its is used by the sql method some time its create error but some runs good

DELIMITER $$
 CREATE TRIGGER update_count
   AFTER UPDATE ON ext_words
     FOR EACH ROW
       BEGIN

          SELECT count INTO @x FROM ext_words_count LIMIT 1;
          UPDATE ext_words_count
          SET count = @x + 1
          WHERE word = NEW.word;

END;
$$
DELIMITER ;

来源：https://stackoverflow.com/questions/15975877/mysql-trigger-on-insert-update-events

标签

mysql

triggers

insert

insert-update