Can someone suggest a way to generate delete queries for various tables linked via foreign key constrains for Oracle ? A solution for SQLServer is mentioned here
Copied description from the original question :
I have the table: DelMe(ID) and there are 30 tables with fk references
to its ID that I need to delete first, is there some tool/script that
I can run that will generate the 30 delete statements based on the FK
relations for me ?
Related
My question is related to the ER-diagram I designed using Oracle SQL developer. I designed this ER-diagram but I don't know how to read the relationships between these tables.
I have created this ER diagram:
ER Diagram
As it can be seen that these relations don't look like those normal one to many or many to one relations. Can anyone please help me how to read the relation between SYS.GENERAL_LEDGER_ACCOUNTS and SYS.INVOICE_LINE_ITEMS? Thanks in advance
The relationship is described by the foreign key:
ALTER TABLE invoice_line_items
ADD CONSTRAINT line_item_fk_accounts
FOREIGN KEY (account_number)
REFERENCES general_ledger_accounts(account_number);
Defines a foreign key with the name line_item_fk_accounts on the column account_number which references the account_number of the general_ledger_accounts.
Assuming that it is notNULL then this is a many-to-one relationship such that each row of invoice_line_items has a relationship to exactly one row in the general_ledger_accounts and there can be many invoice_line_items for each general_ledger_accounts.
Similarly, line_items_fk_invoices is a many-to-one constraint with many invoice_line_items each referencing one row of the invoices table.
Aside: NEVER modify the system schemas. If you do you risk making the database unusable and invalidating any support contract that you have with Oracle. Instead, you should create a user and then work in that schema.
I have created database tables manually and i have also created foreign key constraints in tables manually without using migration. now when i am going to delete a record it giving me following error-
Integrity constraint violation: Cannot delete or update a parent row:
a foreign key constraint fails
Note: i can't use migration because database was already created.
Use ON DELETE CASCADE and ON UPDATE CASCADE on foreign keys, like:
...(create/alter Children table query)...
CONSTRAINT FK_ParentChild
FOREIGN KEY (parent_id) REFERENCES Parents(id)
ON UPDATE CASCADE ON DELETE CASCADE;
So you don't have to manually delete children before deleting the parent element. All children records will automatically delete along with the deletion of parent record.
I would suggest investigating this further by doing the follow:
On your development environment, write migrations to create the
tables from scratch 2)
Look at the generated schema and compare it
to the schema of your existing production tables
Note the
differences between the two schema and write migrations to correct
the production tables.
Note:
If you need to correct the data in the meantime and you are confident that the data integrity of your database is not at risk. You can use the following statements to drop the foreign key checks whilst you correct the data.
SET FOREIGN_KEY_CHECKS = 0;
SET FOREIGN_KEY_CHECKS = 1;
I can't stress enough, remember to turn on your foreign key checks once you are finished and do not do this on a production database. Take a copy of the database and try things locally until you are confident that your corrections are 100% safe ;)
I apologize if I repeat the question, but I did not find a similar one.
I have added a unique constraint on an already existent table. We use MariaDB.
I have used the annotation:
#Table(uniqueConstraints={#UniqueConstraint(name="autonomy_name_energyType", columnNames={"autonomy","name","energyType"})})
The unit tests pass, but in the DB I am still allowed to create duplicates.
Do I need an ALTER table too? By checking the table I can see there are no constraints added to it.
Thanks
As explained in these SO posts :
Unique constraint not created in JPA
#Column(unique=true) does not seem to work
An explicit alter table query is needed for ur constaints to take effect on the db level.
As an extra info, it would have worked if the table was being re-created via JPA. see :
Add a unique constraint over muliple reference columns
I have a migration script in between 2 different schema database. The script does 3 things:
Disable constraint
Insert record from old schema to new schema
Enable constraint
During enable constraint, it encouter ORA-02298 - Parent keys not found: at the following 2 tables:
ALTER TABLE COUNTRY ENABLE CONSTRAINT COUNTRY_FK1;
ALTER TABLE EMPLOYEE ENABLE CONSTRAINT EMPLOYEE_FK7;
Anything went wrong in the table structure definition of these 2 tables?
It appears you are migrating detail records without ensuring that all the foreign key values are present in the referenced tables. If this is the case then you need to migrate records from REGION#SOURCE_DB into REGION#TARGET_DB before you migrate the COUNTRY records.
I'm currenly developing on Oracle. I have several tables for which I defined FOREIGN KEY constraints. I have already read this SQL Server-oriented and this MySQL-oriented questions but I could find none about Oracle.
So the question is always the same: in order to optimize query performance, for those columns for which I create a FOREIGN KEY constraint, do I also have to create an explicit secondary index? Doesn't Oracle automatically create an index on FOREIGN KEYed columns to boost performances during JOINs?
I usually perform queries in which the WHERE clause compare against those columns.
No, Oracle doesn't automatically create indexes on foreign key columns, even though in 99% of cases you probably should. Apart from helping with queries, the index also improves the performance of delete statements on the parent table.