MySQL trigger On Insert/Update events

Question

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..?

Solution 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;   

Solution 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 ;

Comments

[Grijesh Chauhan]

You may like to view this, MySQL Fire Trigger for both Insert and Update Did my solution worked ? What was the result I would like to improve. Remember you can't update same table on which you calls trigger in MySQL

[Drewness]

@GrijeshChauhan - Thanks for the link! I am not able to get your answer working, but that is because I am new to conditional statements in MySQL, not because of your solution.

[Drewness]

I mean that when ext_words is updated, if the word is not in ext_words_count then I want to insert it and make the count 1. Otherwise if the word is in ext_words_count, increase the count by 1...

[Grijesh Chauhan]

Got it of-course for this my query will not work wait...

[Ujjwal Prajapati]

I have a quick question here. If you are storing the words in comma seperated form in some other table like "this, that", can we write a trigger on this table to split the value and store it in ext_words and ext_words_count?

[Grijesh Chauhan]

nice So which form helped you DB.exchange?

[Drewness]

Never heard from anyone. :( I was just browsing through some of the articles. Thanks again for all of your help and pointing me to the other site!

[Kiwi]

This trigger works fantastically in my MySQL server to filter out redundant inserts.