I'm new to programming so please forgive my ignorance. I'm trying to get MySQL tables to update each other. For example: When I insert data into a Primary Key column in one table, it does not appear in it's Foreign Key column in another table.
Does anyone have any advice on this issue?
Thank you!
Additional Information: I used phpMyAdmin to create my tables and then added SQL code to create the Foreign Keys. Example of code is below.
ALTER TABLE CourseSchedule
ADD FOREIGN KEY (CourseId)
REFERENCES Course(CourseId)
I believe what we have here is a slight misunderstanding of the documentation.
For storage engines supporting foreign keys, MySQL rejects any INSERT
or UPDATE operation that attempts to create a foreign key value in a
child table if there is no a matching candidate key value in the
parent table.
When an UPDATE or DELETE operation affects a key value in the parent
table that has matching rows in the child table, the result depends on
the referential action specified using ON UPDATE and ON DELETE
subclauses of the FOREIGN KEY clause. MySQL supports five options
regarding the action to be taken, listed here
What your foreign key actually does is to make sure that you cannot insert values into your CourseSchedule table that do not correspond to an entry in the Courses table.
To give you an example, suppose you were to try to enter schedule a python course for every wednesday at 9:00 but you dont' actually have an entry for python in your Courses table. Then mysql will refuse to create that entry. Mysql cannot do the reverse. It doesn't know details about your python course. So it cannot automatically create a entry in the Courses table for you. Similarly, if oyu created an entr in the courses table. Mysql cannot automatically create a CourseSchedule for you because it doesn't know at what time it should be scheduled.
I'm new to MySQL and databases in general. I've been tasked with manually moving an old database to a new one of a slightly different format. The challenges include transferring certain columns from a table in one database to another database of a similar format. This is made further difficult in that the source database is MyISAM and the destination is InnoDB.
So I have two databases, A is the source and B is the destination, and am attempting to copy 'most' of a table to a similar table in the destination database.
Here is the command I run:
INSERT INTO B.article (id, ticket_id, article_type_id,
article_sender_type_id, a_from, a_reply_to, a_to, a_cc, a_subject,
a_message_id, a_in_reply_to, a_references, a_content_type, a_body,
incoming_time, content_path, valid_id, create_time, create_by,change_time,
change_by)
SELECT id, ticket_id, article_type_id, article_sender_type_id,
a_from, a_reply_to, a_to, a_cc, a_subject, a_message_id, a_in_reply_to,
a_references, a_content_type, a_body, incoming_time, content_path,
valid_id, create_time, create_by, change_time, change_by
FROM A.article
WHERE id NOT IN ( 1 );
Error:
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`helpdesk`.`article`, CONSTRAINT `FK_article_ticket_id_id` FOREIGN KEY (`ticket_id`) REFERENCES `ticket` (`id`))
The reason for making the command so wordy is that the source has several columns that were unnecessary and so were pruned out of the destination table. The WHERE id NOT IN ( 1 ) is there so that the first row is not copied (it was initialized in both databases and MySQL throws an error if they both have the same 'id' field). I can't tell by the error if it expects 'ticket_id' to be unique between rows, which it is not, or if it is claiming that a row does not have a ticket_id and so can not be copied which is what the error seems to most often be generated by.
I can post the tables in question if that will help answer, but I am unsure of the best way to do that, so some pointing in the right direction there would be helpful as well.
Posts I looked at before:
For forming the command
For looking at this error
Thanks!
You'll want to run a SHOW CREATE TABLE on your destination table:
SHOW CREATE TABLE `B`.`article`;
This will likely show you that there is a foreign key on the table, which requires that a value exist in another table before it can be added to this one. Specifically, from your error, it appears the field ticket_id references the id field in the ticket table. This introduces some complexity in terms of what needs to be migrated first -- the referenced table (ticket) must be populated before the referencing table (article).
Without knowing more about your tables, my guess is that you haven't migrated in the ticket table yet, and it is empty. You'll need to do that before you can fill in the B.article table. It is also possible that your data is corrupt and you need to find which ticket ID is present in the article data you're trying to send over, but not present in the ticket table.
Another alternative is to turn off foreign key checks, but if possible I would avoid that, since the purpose of foreign keys is to ensure data integrity.
I want to save all rows get deleted from db in a different table , So once in a day i will run a php command and deleted all related files from server.
I have created a trigger to save deleted row in to a table and it working fine but table rows get delete due to foreign relationship not get save.
I think triggers are not execute on rows get deleted due to foreign key constrain.
please help
You need to alter the trigger on your master table. It should backup all the child records first and then the master table record. Instead of having multiple triggers for all child tables you can try to achieve it using a single trigger.
I have just discovered my database which has been moved between a few servers in the last few months was, in one of the database dumps, converted to myisam and all the foreign key constraints nuked (not impressed). I've converted all the tables back to innodb with a php script but now I'm finding half the constraints are failing to add.
Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`identicar2`.<result 2 when explaining filename '#sql-2a7_c0'>, CONSTRAINT `#sql-2a7_c0_ibfk_1` FOREIGN KEY (`feature_sk`) REFERENCES `tbl_feature_list` (`feature_sk`))
I'm lost now, I can't go through thousands of records manually. what is the best thing to do in order to get my database back into shape?
I can provide table structures if you want but I imagine any solution will be independant of the exact structure anyway
The simplest solution: (containing the obvious danger of losing data you may want to keep)
UPDATE table
SET fkColumn = NULL
WHERE fkColumn NOT IN (SELECT referenceColumn FROM referencedTable)
If you just want to find them:
SELECT *
FROM table
WHERE fkColumn NOT IN (SELECT referenceColumn FROM referencedTable)
I´m using linq to sql and I have a lot of tables with foreign keys leading to the UserId.
Is it possible to have some of these foreign tables cleaned upon deletion.
For example I want the users profile (other table) to be deleted automatically with the user but not the users forum posts.
Is this possible or do I have to handle this with code?
I think this link is very usefull.
LINQ to SQL does not support or
recognize cascade-delete operations.
If you want to delete a row in a table
that has constraints against it, you
must complete either of the following
tasks:
Set the ON DELETE CASCADE rule in the foreign-key constraint in the
database.
Use your own code to first delete the child objects that prevent the
parent object from being deleted.
I am not sure with code, but couldn't you set the Cascade on Delete option in SQL?