So this should be a fairly straight forward trigger, but my MySQL isn't great, so it's undoubtably a failure on my part.
It's not updating the stats table at all, even though it should be;
DROP TRIGGER countryUpdate;
DELIMITER //
CREATE TRIGGER countryUpdate AFTER INSERT ON stats
FOR EACH ROW BEGIN
DECLARE NewIP varchar(16);
DECLARE NewCountry varchar(80);
SET NewIP = inet_aton(new.vis_ip);
SET NewCountry = (SELECT country FROM iptocountry WHERE lower_bound <= NewIP AND upper_bound >= NewIP)
UPDATE stats
SET Country = NewCountry
END //
DELIMITER;
Well, first off, your UPDATE—if it works at all—is changing all rows in the stats table, and its doing that for each row inserted. That really doesn't make much sense. At minimum, you want to add a where clause to only hit the one row you've just inserted.
Apparently, though, that can't work at all in MySQL, because "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." (Look under “Restrictions for Stored Functions”)
So, instead, you need to use a a before insert trigger, and do a SET new.country = NewCountry to fix the row up before its ever inserted.
Related
I was trying to create trigger which can update value of column user_count of table user_details using value of u_count of table user_info.
CREATE TRIGGER `test`
AFTER INSERT ON `user_details` FOR EACH ROW
BEGIN
DECLARE default_user_count int(11);
SELECT u_count INTO #default_user_count FROM
user_info WHERE user_info.id= user_details.id_c;
IF user_details.user_count= 0
THEN UPDATE user_details SET
user_count = default_user_count
WHERE user_details.id_c = user_info.id;
END IF;
END
Trigger saved successfully but when i tried to insert value in both table it is preventing to insert record into user_details means no row inserted in 2 this table, if we delete trigger then its working.
Can anyone let me know wrong with this trigger?
THanks,
M.
It's not really clear what you're trying to accomplish, but it seems like it's something like what we have below.
There are numerous errors in and ambiguities in your trigger.
Confusion on variables -- DECLARE default_user_count INT(11); does not declare the user-defined variable #default_user_count. It declares the program variable default_user_count. The # prefix references an entirely different variable scope and namespace.
SELECT and UPDATE from the table which invoked the trigger doesn't usually make sense (SELECT) or is completely invalid (UPDATE).
With in a trigger, you are operating FOR EACH ROW -- that is, for each row included in the statement that invoked the trigger. Inside an INSERT trigger, the NEW values for the row are in a pseudo-table/pseudo-row accessible via the alias NEW. For UPDATE triggers, there are NEW and OLD row values, and for DELETE triggers, just OLD.
AFTER INSERT doesn't seem to make sense. I think you're looking for BEFORE INSERT -- that is, while processing an INSERT INTO ... query, before the newly-inserted row actually gets written into the table, modify its values accordingly. The resulting row contains the original values except where the trigger has modified them.
SELECT ... INTO a variable is a practice you should not get into the habit of, because it can bite you in a way a scalar subquery can't, by leaving a variable unexpectedly unaltered instead of setting it to NULL as would be expected. In this case, it would have made no difference, but it's still a caution worth mentioning... and in this case, I've eliminated that intermediate variable altogether, so the subquery is the only option.
If you are trying to set a value in this table using a value found in another table, all you need to do is SET NEW.column_name equal to the value you want used in the row instead of the value provided with the insert statement.
CREATE TRIGGER `test`
BEFORE INSERT ON `user_details` FOR EACH ROW
BEGIN
IF NEW.user_count = 0 /* maybe also >> */ OR NEW.user_count IS NULL /* << this */ THEN
SET NEW.user_count = (SELECT ui.u_count
FROM user_info ui
WHERE ui.id = NEW.id_c);
END IF;
END
Again, it's unclear how the two tables are connected based on the content of the original question, but this appears to do what you're trying to accomplish.
I'm fairly new to triggers and have already tried searching for a solution to my question with little results. I want to update a single row's start time column whenever it's active column is set to 1.
I have two columns ACTIVE (number) and START_TIME (timestamp) in my_table. I would like to create a PL/SQL trigger that updates the START_TIME column to current_timestamp whenever an update statement has been applied to the ACTIVE column - setting it to 1.
So far I have only seen examples for inserting new rows or updating entire tables which isn't what I'm looking to do. I'd have thought there would be a fairly simple solution to my problem.
This is what I've got so far from other examples. I know the structure of my solution is poor and I'm asking for any input to modify my trigger to achieve my desired result.
CREATE OR REPLACE TRIGGER routine_active
AFTER UPDATE ON my_table
FOR EACH ROW
WHEN (my_table.ACTIVE = 1)
begin
insert my_table.start_time = current_timestamp;
end;
\
you can use like this .it may help you
write the update query instead of insert query
CREATE OR REPLACE TRIGGER routine_active
AFTER UPDATE ON my_table
FOR EACH ROW
WHEN (new.ACTIVE = 1)
begin
update my_table set start_time =current_timestamp;
end;
I think it should be a BEFORE UPDATE, not AFTER UPDATE, so it saves both changes with a single action. Then you don't need the INSERT or UPDATE statements. I also added the "OF active" clause, so it will only start this trigger if that column was updated, which may reduce the workload if other columns get updated.
CREATE OR REPLACE TRIGGER routine_active
BEFORE UPDATE OF active ON my_table
FOR EACH ROW
BEGIN
IF active = 1
THEN
:NEW.start_time = current_timestamp;
END IF;
END;
Trying to get a trigger to work that refuses to I think it has to be setup as a procedure for it to work which I've never worked with before could anyone tell me how I would go about this? The trigger doesn't show errors when adding but just doesn't do anything
** It now does work apart from changing processed to 0)
UPDATE product
INNER JOIN ebaylinked ON ebaylinked.ebay_ID = product.eBay_ID
SET product.product_stock = product.product_stock - NEW.QuantitySold,NEW.Processed=0
WHERE product.eBay_ID = NEW.ebay_ID and NEW.Processed = 1
First of all, find a more descriptive name for your trigger ;).
Now for the actual problem, your references to the columns in ebaylinked in your trigger code are pretty much mostly wrong. To use the values in the record you just updated, you need to use the pseudorecord NEW, which is a single record containing the current row of the table as it will be after the update completes. References like ebaylinked.QuantitySold are ambiguous, as they do not specify which row of data is the correct one.
Also, you cannot refer to other rows in the triggering table. Your clauses SET ... ebaylinked.Processed=0 ... WHERE ... ebaylinked.Processed = 1 are thus both redundant and wrong, since the only row of ebaylinked your row trigger can see is the current one.
Your trigger code should thus be something like
CREATE TRIGGER `ebaylinked_update_product`
AFTER UPDATE ON `ebaylinked`
FOR EACH ROW
UPDATE product
SET product.product_stock = product.product_stock - NEW.QuantitySold
WHERE product.eBay_ID = NEW.ebay_ID;
Note I'm ignoring the processed column since it does nothing useful (provided the triggering insert is wrapped in a transaction), but if you absolutely must use it, you would change your trigger to before row as follows:
DELIMITER //
CREATE TRIGGER `ebaylinked_update_product`
BEFORE UPDATE ON `ebaylinked`
FOR EACH ROW
BEGIN
IF NEW.processed = 1 THEN
UPDATE product
SET product.product_stock = product.product_stock - NEW.QuantitySold
WHERE product.eBay_ID = NEW.ebay_ID;
SET NEW.processed = 0;
END IF;
END;
//
DELIMITER ;
Note the space between DELIMITER and whatever follows it. This directive is necessary in some clients when the trigger body contains multiple statements terminated by semicolons.
Hope that helps.
PS: You could do this with the trigger calling a stored procedure, but for something this simple I think it would add more complexity than it would be worth.
What is ebaylinked? You should be getting an error when you define the trigger.
If you want to update the table defined by the trigger, then you should use a BEFORE UPDATE trigger. So, I think you intend:
DELIMITER $$
CREATE TRIGGER `Update` BEFORE UPDATE ON `ebaylinked`
FOR EACH ROW
BEGIN
UPDATE product p
SET p.product_stock = p.product_stock - new.QuantitySold
WHERE p.eBay_ID = new.ebay_ID AND new.Processed = 1;
SET new.Processed = 0;
END; $$
DELIMTER ;
I have been trying to create a Trigger, however my attempts have been unsuccessful. I seem to be getting an error (#1064), which I have no solution for. Can somebody explain or demonstrate any faults in the syntax.
Let me specify:
I have delivery_id as primary key in delivery table,
I also have delivery_id as a foreign key in entry_log table.
By comparing both id's(if true), will return a text referring to the output of the bit (either 0 or 1)
DELIMITER //
DROP TRIGGER IF EXISTS entry_trigger//
CREATE TRIGGER entry_trigger BEFORE INSERT ON entry_log
FOR EACH ROW
BEGIN
DECLARE #xentry VARCHAR(45)
DECLARE #inta bit
SET #inta = SELECT allowed
FROM delivery
WHERE delivery.delivery_id = entry_log.delivery_id;
CASE
when #inta = 0 then #xentry = 'Acces Denied'
when #inta = 1 then #xentry = 'Acces Allowed'
END CASE
INSERT INTO entry_log(entry_time,access_allowed) VALUES(now(),#xentry);
END
//
This is assuming that you use MySQL. In the body of the trigger you use
WHERE delivery.delivery_id = entry_log.delivery_id;
I think you want to compare to the entry_log entry that the trigger is running on, right? In that case you must use this syntax:
WHERE delivery.delivery_id = NEW.delivery_id;
see here for more examples.
UPDATE
I see that also you try to do an INSERT INTO entry_log within the TRIGGER. This will of course not work, because you would create an infinite recursive loop. Within the
body of the trigger you can do unrelated table access, but not into the table you are inserting. You can change the values to be inserted by the trigger by setting NEW.xyz = whatever
UPDATE 2
I doubt, that your CASE statement is correct. At least it must end with END CASE. You can use IF here, since you don't have many cases to address. If you must use CASE this post might help you: MYSQL Trigger set datetime value using case statement
UPDATE 3
I am not sure, but I think you need brackets around the variable setting statement. try this trigger definition:
DELIMITER //
DROP TRIGGER IF EXISTS entry_trigger//
CREATE TRIGGER entry_trigger BEFORE INSERT ON entry_log
FOR EACH ROW
BEGIN
SET #inta = (SELECT allowed
FROM delivery
WHERE delivery.delivery_id = NEW.delivery_id);
SET NEW.access_allowed = #inta;
SET NEW.entry_time = NOW();
END
//
Note, that this is written out of my head, so beware of syntax errors in my script.
I'm trying to create a trigger that will automatically increase the year column by 1 when the month column is 12, and then empty the month column.
But I don't understand triggers that well and I'm confusing myself in my attempts, so I was hoping someone could look over this code to see if it would work or suggest improvements:
CREATE TRIGGER aging BEFORE UPDATE ON dogs
FOR EACH ROW
DELETE FROM dogs WHERE month = 12;
UPDATE year SET year = year+1;
Thanks!
Two things to point out...
First, a trigger is clearly the wrong choice for what you want to do. Not only because the trigger can be avoided by calculating the age on the fly based on birth of date. But also, because a trigger only affects the rows that are affected by the corresponding statement. Don't be fooled by the FOR EACH ROW. You write something like
UPDATE table SET whatever = whatever WHERE month = 12;
and all the rows where month = 12 is true are affected. What you seem to want to do, is to update the whole table to check if in some rows your condition is true. Not only is this a performance nightmare, you are also restricted to one trigger (per event) per table. Meaning you can have i.e. one BEFORE UPDATE and 1 AFTER UPDATE but not 2 BEFORE UPDATE.
The second thing to note is, that you can't issue an UPDATE statement in an UPDATE trigger. This would cause an infinite loop :)
Instead you use the aliases NEW and OLD. NEW refers to the value of a column given by the UPDATE statement and OLD refers to the value of the column before the UPDATE statement was executed.
In your case (althoug it's hopefully clear by now, that you shouldn't use the trigger in this case), one would write the trigger like this:
Given this initial statement
UPDATE myTable SET whatever = whatever;
which updates the whole table, this trigger
DROP TRIGGER IF EXISTS [whatever you call this thing];
DELIMITER ##
CREATE TRIGGER aging BEFORE UPDATE ON dogs
FOR EACH ROW
IF (month = 12) THEN /*month refers to the column here, not a variable like in Gordon's answer*/
SET NEW.year = OLD.year+1;
SET NEW.month = 1;
END IF;
END ##
would update the columns correctly.
I've never created a trigger before, but I just read through the docs. This is my attempt...
DELIMITER ||
DROP TRIGGER ID EXISTS [whatever you call this thing]
||
DELIMITER ##
CREATE TRIGGER aging BEFORE UPDATE ON dogs
FOR EACH ROW
DECLARE month integer;
IF (month = 12) THEN
-- DELETE FROM dogs WHERE month = 12;
-- this will delete the record; probably not what you want
UPDATE year SET year = year+1;
UPDATE month SET month = NULL;
END IF;
END;
##