I'm beginer and I'm working on oracle 12c database so, In my database project I want to apply cascade on delete and on update simultaneously as i did in mysql but when i apply tha same technique in oracle it show me the error so how can i do that?
There is no ON UPDATE CASCADE on Oracle. While you can probably argue updating a table's primary key is valid in SQL, you probably should not, hence the decision of Oracle not to implement it.
More info here:
https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:5773459616034
EDIT: As discussed in comments below, think of that constraint as a way Oracle prevents people from doing something wrong (updating primary keys).
The correct way to handle the case of a primary key that might be updated is to create a separate field that will act as the surrogate primary key. The surrogate key, of course, is immutable.
The danger of using a natural key as primary key is discussed there.
Related
I want to migrate a Tarantool table to a different format. Currently (Tarantool 2.8), this must be done manually, by creating a new table, copying the data over, dropping the old table and renaming the new table to the old name. That also means dropping all foreign keys referencing the old table and creating new ones. But an unrelated limitation is that I can't create foreign keys on tables unless those tables are also empty.
Is there any way to solve this other than just not using foreign keys at all?
EDIT: I suppose I could emulate FKs with triggers. Are there any limitations with triggers that would make such emulation impossible?
I wanted to understand that if we drop a PRIMARY KEY using online then what will be the situation for ongoing transactions. Will the maintain data integrity? ideally not cause we have dropped PK. But what could be the real scenario from dropping constraints using online or how we can prevent data conflicts while doing so.
In Oracle, you can keep index but drop Primary Key. In this way you can prevent data conflicts.
ALTER TABLE TBL DROP PRIMARY KEY KEEP INDEX
after that you can add new primary key or unique constraint (whatever it is) and drop former unique constraint
The diagram has over 40 tables, most of them have a primary key defined.
For some reason there is this one table, which has a primary key defined, but that's being ignored when I export the model to a DDL script.
This is the "offending" key (even though it's checked it is nowhere to be found on the generated DDL script):
Has anybody had the same problem? Any ideas on how to solve it?
[EDIT] This is where the key is defined:
And this is the DDL preview (yes, the primary key shows up there):
This is what happens if I try to generate the DDL for just that table (primary key still not generated):
I was finally able to identify and reproduce the problem.
It was a simple conflict of constraints.
Table MIEMBROS had a mandatory 1 to n relationship (foreign key) from another table on its primary key column and vice-versa (there was a foreign key on MIEMBROS against the other table's primary key).
This kind of relationship between two tables makes it impossible to add a record to any of them: The insert operation will return an error complaining about the foreign key restriction pointing the other table.
Anyway I realized that one of the relationships was 0 to n so I simply unchecked the "mandatory" checkbox on the foreign key definition and everything went fine.
So, in a nutshell: The Data Modeler "fails" silently if you are defining a mutual relationship (two foreign keys, one on each table against the other table) on non nullable unique columns, by not generating the primary key of one of the tables.
Such an odd behavior, if you ask me!
"This kind of relationship between two tables makes it impossible to add a record to any of them: The insert operation will return an error complaining about the foreign key restriction pointing the other table."
Actually, if you have deferred constraints, this is not impossible. The constraints can be enforced, for example, at commit time rather than immediately at insert time.
From the Data Modeler menu under File, I used Export -> DDL File. The keys appeared in the DDL, then when I went back to the diagram and did DDL Preview, it showed all the missing stuff.
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.
I need to insert records into a table that has no primary key using LINQ to SQL. The table is poorly designed; I have NO control over the table structure. The table is comprised of a few varchar fields, a text field, and a timestamp. It is used as an audit trail for other entities.
What is the best way to accomplish the inserts? Could I extend the Linq partial class for this table and add a "fake" key? I'm open to any hack, however kludgey.
LINQ to SQL isn't meant for this task, so don't use it. Just warp the insert into a stored procedure and add the procedure to your data model. If you can't do that, write a normal function with a bit of in-line SQL.
Open your DBML file in the designer, and give the mapping a key, whether your database has one or not. This will solve your problem. Just beware, however, that you can't count on the column being used for identity or anything else if there isn't a genuine key in the database.
I was able to work around this using a composite key.
I had a similar problem with a table containing only two columns: username, role.
This table obviously does not require an identity column. So, I created a composite key with username and role. This enabled me to use LINQ for adding and deleting entries.
You might use the DataContext.ExecuteCommand method to run your own custom insert statement.
Or, you might add a primary key to a column, this will allow the objects to be tracked for inserts/updates/deletes by the datacontext. This will work even if the column isn't really an enforced primary key in the database (how would linq know?). If you're only doing inserts and never re-use a primary key value in the same datacontext, you'll be fine.