i am new to this topic.
i want something like this.
i have two tables in my sqliteDatabase one is master and another is child.
Now if i delete a record from master suppose i delete a row from master where id=5, then all the records from the child table whose id = 5 deleted automatically.
I don't know how to create triggers and how to apply foreign key constraints so someone please tell me a way to do this in sqlite3 Manager of firefox.
Thanks
You don't need a trigger for that, your foreign key will do that if you define ON DELETE CASCADE:
CREATE TABLE child(
id INTEGER,
some_info TEXT,
master_id INTEGER,
FOREIGN KEY(master_id) REFERENCES master(id) ON DELETE CASCADE
);
See documentation about foreign keys.
EDIT:
If you really need to do it using a trigger, have a look at Foreing Key Triggers.
This page should help:
http://justatheory.com/computers/databases/sqlite/foreign_key_triggers.html
This is a general trigger reference for SQLite
Related
I have a table (multisite network) where I use blog_id as one of the columns which is also needed on some of my custom php functions. Until now, I haven't used FK which should be appropriate for my tables.
So, can I FK to wordpress wp_blogs table? if yes, if ever I delete that blog will it also delete the entries on my other tables that references wp_blogs?
CREATE TABLE wp_blogs (blog_id INT NOT NULL...)
FOREIGN KEY (blog_id)
REFERENCES wp_options(blog_id)
ON DELETE CASCADE;
If you created a table like above then every time when blog_id will remove from wp_options then all rows from wp_blogs will remove too.
When you remove rows from wp_blogs then no rows won't remove from wp_options
Read about ON DELETE CASCADE in MySQL documentation.
I have a script for microsoft sql server database which has hundreds of tables and tables contains data as well. This is the database of a web application.what I want to do is to delete the previous records and reset the primary key to 1 or 0.
I have tried
`DBCC CHECKIDENT ('dbo.tbl',RESEED,0); `
but it does not work for me as in most of the tables the primary key is not identity.
I can not truncate the table as its primary key is being used as FK in many other tables.
I have also tried to add the identity specification in the primary key of the table and run the checkident query and then changing it back to non-identity spec, but after adding the record again it starts from where it left.
Making changes in the code is not an option for me.
please help.
According with your question I am not sure about the main objective, Why? If you need truncate a lot of tables and change their structures to have an Identity property why you can't disabled the FK? . In the past I have used an standard process for rebuild a table and migrate all the information, this represent a group of steps, I would try to help you but you should follow the next steps.
Steps:
1) Disable FK for alter the structure of your tables. You can get the solution for this task in the next link:
Temporarily disable all foreign key constraints
2) Alter the table with the new property Identity, this is a classic process of ALTER TABLE xxxxxx.
3) Execute the syntax that previously posted :
DBCC CHECKIDENT ('dbo.tbl',RESEED,0);
Try to follow this path and if you have any problem only ask us.
You can not truncate table that have relation. You shoud remove relation firstly.
My understanding of this question:
You have a database with tables that you want to empty and next have them use primary key values starting at 0 or 1.
Some of these tables use an identity value and you already have a solution for those (you know you can find out which columns have an identity by using the sys.columns view? Look for the is_identity column).
Some tables do not use an identity but get their pk values from an unknown source, which we can't modify.
The only solution I see, is creating an after insert trigger (or modifying) on those tables that subtracts from the new pk value.
E.g.: your "hidden generator" will generate a next value 5254, but you want the next pk value to become one:
CREATE TRIGGER trg_sometable_ai
ON sometable
AFTER INSERT
AS
BEGIN
UPDATE st
SET st.pk_col = st.pk_col - 5253
FROM sometable AS st
INNER JOIN INSERTED AS i
ON i.pk_col = th.pk_col
END
You'll have to determine the next value and thus the "subtract value" for each table.
If the code also inserts child records into tables with a foreign key to this table, and uses the previously generated value, you have to modify those triggers as well...
This is a "last resort" solution and something I would recommend against in any scenario that has other options. Manipulating primary key values is generally not a good idea.
pls guys...is there a way delete all iDs referenced to particular ID in a database when that particular ID is deleted?
take for instance i have a company data that has list of departments with staff under them and also all those staff have different records under them like attendance, bio data, salary scheme e.t.c.
the way i designed my database is that staffs under a department are referenced to that department using a foreign key and like wise all records under a particular staff is referenced to that staff using a foreign key.
now, is it possible to have a sort of trigger or any other sort of mechanism so that when i delete a staff from the staffs table every other record referenced to that staff will be deleted also.
i would have considered using multi table delete but since am using java sqlite, it doesnt support that from what i read. And i wouldnt like to go through the stress of having to delete all records one after the other from all the tables.
thanks a lot guys
ON DELETE CASCADE could help you. Take a look at the documentation:
CASCADE: A "CASCADE" action propagates the delete or update operation on the parent key to each dependent child key. For an "ON DELETE CASCADE" action, this means that each row in the child table that was associated with the deleted parent row is also deleted.
you just need to reference the row id of the parent table:
CREATE TABLE parentTable(
parent_id INTEGER PRIMARY KEY,
data TEXT
);
CREATE TABLE childTable(
child_id INTEGER,
parent_id INTEGER REFERENCES parentTable(parent_id) ON DELETE CASCADE
);
and I think you would also need to active the foreign keys for this to work:
PRAGMA foreign_keys = ON;
i have two tables Table1 and Table2. Where table1 column primary key is referred to table2 column as foreign key.
Now i have to display a error message of constraint violation when ever i delete records from table2 which is having foreign key column of table1.
If I get it right your column A (say) in table 1 references column B (say) in table 2.
What you can do is set the ON DELETE to NO ACTION which will prevent deletion of records from table 2 if any children of it still exists in table 1.
You can can do this by:
ALTER TABLE TABLE1 ADD FOREIGN KEY (A) REFERENCES TABLE2 (B) ON DELETE NO ACTION;
You don't have a constraint violation if you delete records from the child table and not the parent. It is normal to delete child records. For instance if I have a user table and a photos tables that contains the userid from the users table, why would I want to stop that action and throw an error if I want to delete a photo? Deleting a child record doesn't also delete the parent.
If you really want to do that, then you must do it through a trigger (make sure to handle multiple record deletes) or if the FK is a required field, then simply don't grant permissions to delete to the table. Be aware that this may mean you can never delete any records even when you try to delete. A simple method may be to not have a delete function available in the application.
I suspect what you really need to a to get a better definition of what is needed in the requirements document. In over 30 years of dealing with hundreds of databases, I have never seen anyone need this functionality.
I need to update the primary key for a record but it's also the foreign key in two other tables. And I need the updated primary key to be reflected in the child tables as well.
Here is my query and the error:
begin tran
update question set questionparent = 10000, questionid= 10005 where questionid = 11000;
Error 9/4/2009 10:04:49 AM 0:00:00.000 SQL Server Database Error: The UPDATE statement conflicted with the REFERENCE constraint "FK_GoalRequirement_Question". The conflict occurred in database "numgmttest", table "dbo.GoalRequirement", column 'QuestionID'. 14 0
I don't remember how to go about doing this so that's why I'm here. Any help?
Are your relationships using
ON UPDATE CASCADE
If they are then changing the key in the primary table will update the foreign keys.
e.g.
ALTER TABLE Books
ADD CONSTRAINT fk_author
FOREIGN KEY (AuthorID)
REFERENCES Authors (AuthorID) ON UPDATE CASCADE
You may:
disable enforcing FK constraints temporarily (see here or here)
update your PK
update your FKs
enable back enforcing FK constraints
do it all within a transaction and make sure that if transaction fails, you roll it back properly and still enforce the FK constraints back.
But... why do you need to change a PK? I hope this is an action that is executed rarely (legacy data import or something like that).
If you would like to set the Cascade rule graphically then Set Cascade Rule on SQL Management Studio
Open table in design mode
Click Relationship button from top toolbar
Select the required FK relations (one by one)
Right Side - Expand INSERT or UPDATE Specification
Change the UPDATE Rule to - Cascade
Close and Save, Done!
(Tried on SQL 2008)
As I'm not too confident disabling FK constraints, I prefer too :
Duplicate the row with the old PK with one with the new PK
Update the FKs
Delete the row with the old PK
Advantage : No constraint violated during the process.
Go to foreign Key Relations of each child tables and on Insert and Update specification change delete and update rules to cascade.
create a New row with the same data and a different primary key.
update all the children tables.
remove the row that you repeated its data
And its done.