I think that there was a way that by not making two INSERT statements we could add a row on another table. I don't know if it was about CASCADEing or not but didn't find anything based on the keywords (wrong maybe!) I used.
Currently I've two tables, one is users and the other is data, when a user is created I want a row in data table get added so in this way I can update it later. data columns are all nullable except the uid which is user id on data table -Unique- that respectfully lives in id column of users table.
Any help is appreciated.
Thanks to the guys that triggered me to use a TRIGGER. I wasn't familiar with them at all!
Here is the Trigger, as simple as possible, for the later visitors of this topic:
DELIMITER $$
CREATE
TRIGGER `user_after_insert` AFTER INSERT
ON `users`
FOR EACH ROW BEGIN
INSERT INTO data (uid) VALUES (NEW.id);
END$$
DELIMITER ;
I don't recommend reading docs if you're a newbie in them like me but this page that will help you unserstand more with some examples!
Related
I'm struggling to find proper information on SQL Triggers.
My previous question got removed for it not being specific enough so hopefully this will do better.
I am trying to create a trigger that will assign RoleID 1 to every newly inserted row to my users table.
But I can't seem to figure it out.
AFTER INSERT on users
on EACH ROW
insert into users.RoleID values(1);
This doesn't seem to work.
And the examples and or information regarding triggers all focus on alerts or sending emails after an insert/drop or update.
Can it actually be done?
Any help would be much appreciated.
Cheers!
It looks like you aren't creating you sql trigger with the correct keyword.
Try this
drop trigger if exists before_insert_users;
DELIMITER $$
CREATE TRIGGER before_insert_users
BEFORE INSERT ON users
FOR EACH ROW
BEGIN
SET NEW.RoleID = 1;
END$$
DELIMITER ;
Note: RoleID will need to actually be a column on your table for this to work.
However, a trigger is not the best way to do this... See this SO post : Add a column with a default value to an existing table in SQL Server
I have two table
1: Roll_no Name Address Branch
2: Roll_no Branch Name Percentage Marks
Is it possible in database that when i will add/update/Delete the data from one table it automatically do the operation on another with out front end programming...
As #Gordan said the triggers are the best way to do this.
Follow the below steps to achieve your requirement,
Create Trigger using the below query,
CREATE TRIGGER trigger_name
AFTER INSERT
ON 'User' FOR EACH ROW
Insert into 'UserCreatedTime' values(NOW())
What it meant, After inserting the values into 'User' table insert query for 'UserCreatedTime' table will be triggered automatically.
Please check the youtube video for more details,
https://www.youtube.com/watch?v=oKDqZCkBRZ8
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.
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.
CREATE TRIGGER items_
ON test
after update
AS
begin
INSERT INTO test2(id,namecan)
SELECT id,namecan from test
end
I Have tried with trigger but i didnt get any results so please help me how to deal with it
methods involving two stored procedures are also welcome
You could do it with a stored procedure, but I would use a trigger.
With a stored procedure, I'd perceive you using a cursor on the otherDatabase table to read through the records and compare each with the values in Table1 to determine whether Table1's data needed to be written to Table2, and if so, to do it.
With a trigger, I would simply update the data in Table1 by whatever means, without concerning myself with what the overwriting data is, and in the trigger,
use the old and new values using the ##Inserted & ##Deleted (system) tables to determine if the old values (##Deleted) needed to be written to Table2.
If you don want to use triggers, you can go for this concept..
Let there is a form from which you are inserting the values on a table say register table. And the action of the form in going to servlet MyServlet. In Myservlet
you can first fetch the data from the Register table and store it into the Rsultset object let rs. And after that insert the rs into a new table.
Please let me know if m not clear to u..
Your trigger syntax is wrong
delimiter //
CREATE TRIGGER items_ after update
ON test
for each row
begin
INSERT INTO test2(id,namecan) values (old.id,old.namecan);
end; //
delimiter ;
So this trigger will make an entry to the test2 table every time you update row in the test table with the old row values from test table.
You should call old.id and old.namecan (i assume that table 'test' have 'id' and 'namecan' field)to get the older data. your trigger body should look like this
begin
INSERT INTO test2(id,namecan) value(old.id, old.namecan)
end
'old' will reference to record which you update.