I found this question MYSQL Trigger Update Copy Entire Row
Where the suggestion to use the following code answer partially to my personal question to perform a row backup after altering a DB row:
DROP TRIGGER auditlog
CREATE TRIGGER auditlog AFTER UPDATE ON frequencies
FOR EACH ROW BEGIN
INSERT INTO frequencies_audit select * from frequencies where freqId = NEW.freqId;
END;
The problem is that I like to insert additional information to the backuped row so I thought that add variables could do the trick. My question is, is this the right procedure?
INSERT INTO frequencies_audit select *, #variable, 'my_value' from frequencies where freqId = NEW.freqId;
I know this question is old, but I stumbled upon exactly the same question. For me, just adding the missing fields directly like in:
INSERT INTO frequencies_audit select *,"insert" as operation from frequencies where id = NEW.id
worked fine for me. For more realistic cases, you would have to join.
Related
Hey guys a little question for you.
I'm currently working on SQL Triggers and my goal is to archive logging if there are changes made to our database. For example we got some tables like customers with: name, firstname, placeofbirth and so on. We offer the users to update their own data and want to save the OLD data in a new table for logging reasons. To have only one logging table for all updates the logging table is kind of generic with:
id, timestamp, table_name, column, old_value, new_value.
table_name is the updated table, colum the updated column in this table and all the rest should speak for itself. Therefore it would be great to know not only in which tuple but also in which particular column the update has happened.
My question: Is there a construct like:
create trigger logging_trigger on customer**.firstname** after insert ...
to trigger an action only if there happened an update on let's say the 'firstname' column?
If not is there a smooth solution for handling all possible update cases?
Thank you.
I use a format like you described in my system... Below is how I accomplish it with your required logic.
CREATE DEFINER = CURRENT_USER TRIGGER `testing_schema`.`new_table_BEFORE_UPDATE` BEFORE UPDATE ON `new_table` FOR EACH ROW
BEGIN
IF NEW.ColumnName <> OLD.ColumnName THEN
INSERT INTO HistoryTable (`ColumnName1`, `ColumnName2`, ect..) VALUES (OLD.ColumnName1, OLD.ColumnName2, ect...);
END IF;
END
The main difference In mine is, that I do not have an IF condition. I simply copy the entire row to the history table every time an Update/Delete is made to that row. That way I don't have to maintain any form of logic to handle scenarios of investigating "what changed", I just save the entire row because I know "something" changed.
i'm working on a proyect in mysql and i can't made things work between 2 triggers, what i'm trying to do is
1)
Create a trigger that after inserting values in a table update the data of another table, working
2)
Create a trigger that after updating the aforementioned table, delete the row that detonated the first trigger, not working
I searched the documentation, examples, tutorials, goolge and of course in different posts of the site, but I have not found anything that can guide me or help to solve my problem :(
For the moment i have this
1)
CREATE TRIGGER update1 BEFORE INSERT ON table1
FOR EACH ROW
UPDATE table2 SET table2.value = table2.value +
NEW.value WHERE ac_id = NEW.acc_id
2)
CREATE TRIGGER `delete` AFTER UPDATE ON table2
FOR EACH ROW DELETE FROM table1 WHERE table1.acco_id =
NEW.acc_id
Individually both work, but if I make an insert in table1 the following message appears
Can't update table 'table1' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
sorry for my bad English, any help will be highly appreciated, thanks in advance
The observed error message:
ERROR 2442 (HY000) Can't update table '%s' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
is expected behavior. The triggers shown in the question violate a documented restriction:
A stored function or trigger cannot modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.
Reference: https://dev.mysql.com/doc/refman/5.7/en/stored-program-restrictions.html
To focus that on the specific triggers shown in the question, in the context of a trigger fired by an insert into table1, it is not possible to delete rows from table1. There is no workaround to this restriction.
To "solve this problem" means to step back from the current design, and come up with a different design which achieves the objectives.
Am populating a table using a trigger after an insert event occurs on another table and that worked fine. However i then noticed that the trigger would still insert a new row for existing records. To fix this, I want to create the trigger again but this time it would only fire if a condition is met...but not having previously used triggers in the past am getting a syntax error and not able to identify what am doing wrong. Kindly have a look and help me fix this
CREATE TRIGGER `students_gen_insert`
AFTER INSERT ON `students` FOR EACH ROW
BEGIN
INSERT INTO records (student_id, subject_id)
SELECT new.student_id, subjects.subject_id
FROM subjects
WHERE category = new.class;
END;
Am currently using MySql 5.6.17 version.
It is generally not a good idea to SELECT from the table the trigger is on, and forbidden to UPDATE or INSERT (not that you are doing those). Assuming you are trying to get the values for the row just inserted, the first SET ... SELECT you have is needless; just use NEW.fieldname to get the fields of the inserted row.
The second SET ... SELECT and following condition are a bit confusing. If referential integrity is being maintained, I would think it would be impossible for the records table to refer to that particular student_id of the students table at the point the trigger is executed. Perhaps this was to avoid the duplicate inserts from the trigger's previous code? If so, it might help for you to post that so we can pinpoint the actual source of redundant inserts.
I've already, searched and read, many answers about this issue , but couldn't get a clear answer on how to do this.
My query is the following:
DELIMITER //
CREATE TRIGGER `Stock_Update` AFTER INSERT ON `Store_db`.`Product_Supply` FOR EACH ROW
BEGIN
UPDATE `Store_db`.`Stock` AS `ST`
SET `ST`.`Stock_Quantity` = `ST`.`Stock_Quantity` + `Product_Supply`.`Supply_Quantity`
WHERE `ST`.`Product_ID` = `Product_Supply`.`Product_ID`;
END//
DELIMITER ;
Thanks In Advance.
P.S. A More Generic Answer would be nice too and might be helpful for others as well
From within a trigger on a given table, all references to fields of this table must be prefixed by either NEW. or OLD., which refers respectively to the value of this field after or before the change.
In your case, you probably want to add the newly inserted quantity to your existing stock: use NEW.Supply_Quantity (do not mention Product_Supply, this is already implied by the NEW keyword).
Likewise, you certainly want to use NEW.Product_ID in your condition.
Notice that NEW is not available in a trigger on deletion, like OLD in a trigger on insertion.
I'm trying to create a database with history in mind (experience shows you'll have to do this one day or another).
I've asked here database-design-how-to-handle-the-archive-problem but there's no better anser than the link here.
My problem is about where to do the code and technically, how (MySQL gives me headaches). First I've started doing this in Php: before doing any insert, duplicate the record mark it as "obsolete" then modify the record.
But there's a dependency problem (manytomany and manytoone associations must be updated as well) which implies coding (one way or another) all the dependancies and updates that come with the tables (which is not acceptable).
So I'm thinking about doing all the work on the database server side. This would greatly simplify my Php code.
The problem is that I have to "archive" the current record before modifying it. To do so, the code must be in a trigger "before update".
Here's my code:
DELIMITER ;;
DROP TRIGGER IF EXISTS produit_trigger_update_before;
CREATE TRIGGER produit_trigger_update_before
BEFORE UPDATE ON produit
FOR EACH ROW BEGIN
/* */
INSERT INTO produit SET
id_origine = OLD.id_origine,
date_v_creation = OLD.date_v_creation,
date_v_start = OLD.date_v_debut,
date_v_end = NOW(),
...
last_record = OLD.last_record;
/* Dependancies : */
SET #last=LAST_INSERT_ID();
UPDATE categorie_produit SET id_produit=#last
WHERE id_produit = OLD.id;
UPDATE produit_attribut SET id_produit=#last
WHERE id_produit = OLD.id;
END;;
DELIMITER ;;
If I get this code working, all my problems are gone. But damn it, it's not working:
mysql> update produit set importance=3;
ERROR 1442 (HY000): Can't update table 'produit' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.
mysql> Bye
In this page there's a working sample, which uses INSTEAD OF UPDATE clause in the trigger. MySQL doesn't seem to support this.
So my question is both conceptual (= have you any other "principle" that could work) and/or technical (= can you make this trigger work).
If I get this code working, all my problems are gone. But damn it, it's not working:
As a rule you can't have a trigger on table A trigger inserts into table A - since that could cause an endless loop. (Trigger mutation in Oracle terms)
Personally I would not do this using triggers. Triggers can do "audit logging" - but this is not what you want here.
I suggest you solve it programatically - either with a PHP function or a MySQL stored procedure (whatever your preference) that you call something like "ModifyProduit".
The code would then do basically what you have the trigger above do. (It might be easier to just have the code set date_v_end on the current row, and then insert a completly new row. That way you don't have to mess around with updating your referenced tables)
you can do history of a table with an auxiliary table like this (i've done this for many tables on mysql and the speed is very good):
table produit_history has the same structure as produit + 2 additional columns: "history_start DATETIME NOT NULL" and "history_stop DATETIME DEFAULT NULL".
there are 3 triggers on produit table:
AFTER INSERT: in this trigger there is a simple insert into produit_history of the same data with history_start = NOW() and history_stop = NULL (NULL means the current row is valid)
AFTER UPDATE: this trigger performs two queries. The first is un update like this:
UPDATE produit_history set history_stop = NOW() WHERE id_origine = OLD.id_origine AND history_stop IS NULL;
The second query is an insert identical to the one in the AFTER INSERT trigger.
AFTER DELETE: this triggers there is a simple update which is identical to the one in the AFTER UPDATE.
You can then query this history table and obtain snapshots at whatever time you're interested in with the following where condition:
WHERE (history_start <= "interesting_time" AND (history_stop IS NULL OR history_stop > "interesting_time"))