I have this trigger to update a single field in a journal table after each update, but I need to update ALL columns in related row in journal at once, not by naming each of them and separating by comma, how can I do that?
DELIMITER //
CREATE TRIGGER sfo_clone_update_subtotal_invoiced AFTER UPDATE ON sales_flat_order
FOR EACH ROW BEGIN
update sales_flat_order_journal set subtotal_invoiced=NEW.subtotal_invoiced where entity_id=new.entity_id;
END;
DELIMITER ;
UPDATE syntax allows you to set multiple columns, separated by commas.
update sales_flat_order_journal
set subtotal_invoiced = NEW.subtotal_invoiced,
other_column1 = NEW.other_column,
other_column2 = (/* constant expression, not based on NEW */),
other_column3 = (SELECT ...scalar expression from some other tables... LIMIT 1),
updated_at = NOW()
where entity_id = new.entity_id;
You can access NEW.other_column to get the values of the same row that spawned the trigger.
You can DECLARE local variables in your trigger body to help calculate complex values.
You can use SELECT statements in your trigger body to query values from other rows or other tables, as long as you use a scalar SELECT that returns one row and one column.
If you need a more complex update that's too difficult to do in a trigger, I would do that in application code, not a trigger.
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;
There is a declared MySQL function GETUSERID() returning an integer value. How to make a record insert faster: setting the value from inside a query like
INSERT INTO ttable
(idtoset, some_other_field...)
VALUES (GETUSERID(), value1...);
or call
INSERT INTO ttable
(some_other_field...)
VALUES (value1...);
and fill idtoset by a trigger that fires before insert?
What if the query is performing multiple row insert like
INSERT INTO ttable
(idtoset, some_other_field...)
VALUES (GETUSERID(), value1...),
(GETUSERID(), value2...),
...
(GETUSERID(), valueN...);
?
Edit
I have just investigated the answer of #Rahul.
I created a ttest table with two triggers
CREATE TRIGGER `tgbi` BEFORE INSERT ON `ttest` FOR EACH ROW BEGIN
SET NEW.testint=1;
END;
CREATE TRIGGER `tgbi` BEFORE UPDATE ON `ttest` FOR EACH ROW BEGIN
SET NEW.testint=2;
END;
If I am not mistaken, should the before insert trigger call UPDATE SET the second trigger is expected to fire as well and the created testint value might be =2, but it is =1 in every inserted row. Could that mean that the engine optimises INSERT procedure and sets the value simultaneously with that set manually by query?
Appended on request of #Rick-James. The question is not about the definite function. It is actually about any function. Any function will be called same number of times if the record is inserted from trigger or from INSERT query. That is why I am wondering what is better from the point of MySQL engine - to call it manually setting the value in inserted records or filling it by means of triggers?
CREATE DEFINER=`***`#`***` FUNCTION `GETUSERID`() RETURNS int(10)
BEGIN
DECLARE id_no INT DEFAULT -1;
SELECT `id` INTO id_no FROM `tstuff`
WHERE `tstuff`.`user_name`=
(SELECT SUBSTRING_INDEX(USER(), '#', 1)) LIMIT 1;
RETURN id_no;
END
What is faster? No idea since I haven't done a bench marking on that but doing an direct INSERT operation would better to my knowledge instead of inserting and then perform an UPDATE through trigger.
Does what you are doing currently not working? you can as well make it a INSERT .. SELECT operation like
INSERT INTO ttable (idtoset, some_other_field...)
SELECT GETUSERID(), value1..., valuen FROM DUAL;
In past versions of MySQL, using a before insert trigger to populate a not nullable column didn't work as MySQL was evaluating the provided columns before the trigger. That's why whenever I have such a situation, I usually tend to go with functions instead of triggers.
From a performance point of view, since the before insert trigger is evaluated before actually writing data so the time needed to perform this is almost the same as immediately getting the value with the function and without trigger. But if all you are doing in the trigger is set the user ID, then I really see no reason to use a trigger.
I need to update a table with pre-calculated values from tables where data can be added/updated/deleted.
I could use
insert into precalculated(...)
select ... from ...
on duplicate key update ...
to add/update the pre-calculated table but is there an optimized method to delete the obsolete rows ?
I think you should create a stored procedure that deletes the data of your related tables if and only if the records fulfill a condition.
There's not enough information in your question to design the procedure, but I can give you a little example:
delimiter $$
create procedure delete_orphans()
begin
declare id_orphan int;
declare done int default false;
declare cur_orphans cursor for
select distinct d.id
from data as d
left join precalculated as p on d.id = p.id
where p.id is null;
declare continue handler for not found set done = true;
open cur_orphans;
loop_delete_orphans: loop
fetch cur_orphans into id_orphan;
if done then
leave cur_orphans;
end if;
delete from data where id = id_orphan;
end loop;
close cur_orphans;
end$$
delimiter ;
This procedure will delete every row in the data table that does not have at least one related row in the precalculated table.
Of course, this approach might be inneficient, because it will delete the rows one by one, but as I said this is only an example. You can customize it to fit your needs.
You can call this procedure from a trigger if you want (with call delete_orphans()).
Hope this helps.
Since you are always adding or updating rows that exist in these other tables, and you want to remove any rows that don't exist, why don't you just :
DELETE FROM precalculated
insert into precalculated(...)
select ... from ...
on duplicate key update ...
Always starting clean means you don't have to worry about orphans later.
You could add triggers for insert, delete and update on the main tables that maintains precalculated.
When inserting or updating the same code can be used to calculate the values and issuing a replace into precalculated (...) values (...)
When deleting it's probably the same, with the addition that you'll also delete rows from precalculated that are orphans. Be smart here and use values from the original delete to query precalculated for orphans instead of doing a table scan.
I may have found my solution using rename.
so basically, I will do a simple insert select to the temporary table and then
rename precalculated to precalculated_temprename, precalculated_temp to precalculated, precalculated_temprename to precalculated_temp;
truncate precalculated_temp;
need some tests but it seems the rename operation is fast and atomic.
I have a MySQL trigger using the BEFORE INSERT ON table that calculates a value and updates the same table after a user inserts values in specific columns. This works as expected. But a user makes a mistake in their entry and fixes their error and I want to write a trigger that will update the calculated value after the error has been fixed. Is there a way to achieve this?
A BEFORE UPDATE ON table trigger has access to the existing values in the row as well as newly supplied values, and can set the value of any column in the table, based on whatever conditions and expressions we want.
For example, it's possible to test whether the value of one or more columns of concern has been modified, and then set some other column to some expression.
DELIMITER $$
CREATE TRIGGER my_before_update_trigger
BEFORE UPDATE ON my_table
FOR EACH ROW
BEGIN
IF NOT ((NEW.col1 <=> OLD.col1) AND (NEW.col2 <=> OLD.col2)) THEN
SET NEW.col3 = NEW.col1 * NEW.col2 ;
END IF;
END$$
DELIMITER ;