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;
Related
Old version
I have a Person table and the table Company.
both tables have a column Id (Identity)
Table Company have Ids of 1 to 165
In the table Person have Ids 1 until 2029
New Version
In the new version of the system, was created a table Entity.
This table contains the records of the Companies and People
The Company and Person tables will be maintained, referring to the Entity table.
The Id in table Entity will be the same in Company or Person table
Question
Both tables have multiple relationships with other tables.
Table Entity (as well as others) has a column ID (identity).
The problem is that the Id were repeated when the two tables together (It was to be expected).
How to import without losing relationships?
Attempts
I thought of changing the value of Ids in Company table, starts from 2030.
Thus the Ids would not duplicate when joining the two tables.
But this creates another questions.
How to do this without losing existing relationships?
How to change the Id of a row in the table and this is reflected in all tables which it relates?
I would like to do this using only DDL (SQL Server)
I thought of changing the value of Ids in Company table, starts from 2030. Thus the Ids would not duplicate when joining the two tables.
Create foreign key constraints on the Person table to all related tables (or alter the existing foreign key constraints) with ON UPDATE CASCADE. Then update the Person table and change the values if the id columns - these changes will cascade to the related tables.
To stop further problems, maybe change the identity columns in Person and Company to something like identity( 1000, 3 ) and identity (1001, 3) respectively.
However, I think the best idea is to have a different EntityID column in the Entity table, unrelated to PersonID and CompanyID. The Entity table would also have a column called AltEntityID or BusinessKey that contains the id from the other table and that does not have a unique constraint or a foreign key constraint.
And if you make small modification to your attempt - add new column, say newId, to Company and to Person to manage relation with Entity and leave id columns as is. Why this is the simpliest way? Because new columns shouldnot be identity columns, from one side. From the other side, you can leave all logic of relating other tables with Company and Person intact.
I have a data table with a primary key called OptDefID. When a record in this table is deleted I need to go and delete all records from the Permissions table that have that OptDefID in the defID field (in Permissions). The tricky part for me is that the Permissions table does not have a primary key and holds lots of different kinds of permissions, and has a permissiontype field. I need to delete rows that have the OptDefID AND a permissiontype of OptDef.
Because I need to consider the permissiontype, I don't believe a Foreign Key Constraint is appropriate here (or is it?).
I've also considered creating a trigger, but am unsure how to get the OptDefID passed into the trigger.
I can do this via the application itself, but I feel like this should be a database level solution.
What's the best solution?
Say I want to delete from Permissions where defID is 20 and permissiontype is 'OptDef'. There may be another row in Permissions that has a defID of 20, but has a permissiontype of 'Member'. That show should not be deleted because it pertains to Members and not Opt data.
Storing table names in fields prevents foreign keys from working properly, as you have discovered.
I recommend you fix the root problem and separate these two foreign keys, so each of them can be individually enforced. For example:
CREATE TABLE Permissions (
...
OptDefId int,
MemberId int,
FOREIGN KEY (OptDefId) REFERENCES OptDef ON DELETE CASCADE,
FOREIGN KEY (MemberId) REFERENCES Members ON DELETE CASCADE,
CHECK (
(OptDefId IS NOT NULL AND MemberId IS NULL)
OR (OptDefId IS NULL AND MemberId IS NOT NULL)
)
)
The CHECK makes sure only one of the FKs is non-NULL and only non-NULL FKs are enforced.
Alternatively, you could avoid changing your current design and enforce this "special" FK through a trigger, but declarative constraints should be preferred to triggers when possible - declarative constraints tend to leave less room for error and be more "self-documenting".
In case the OptDefId column is only filled when the record in question references the Permissions table, a foreign key should be appropriate. I.e. you have another column MemberId, which in turn could be a foreign key on a Members table.
It is only when you have a single column - let's call it ObjectId - which takes on other meanings as the contents of the type column change, that you cannot use foreign keys.
In that case, a trigger would probably be the best approach, as you already guessed. I only know about triggers in Oracle PL/SQL, where they are passed in as separate, complete rows representing the old and new state. I guess it will be analogous in MS-SQL-Server.
In addition to using join with SELECT statements, you can also join multiple tables in DELETE & UPDATE statements as well.
As I understand the issue, you should be able to join the Permissions table to the table with the OptDefID column & add a WHERE clause similar to the this:
DELETE MyTable
...
WHERE [Permissions].permissiontype = 'OptDef'
Also, these links may be of interest too:
SQL DELETE with JOIN another table for WHERE condition (for MySQL, but still relevant)
Using A SQL JOIN In A SQL DELETE Statement
Using A SQL JOIN In A SQL UPDATE Statement
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 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
I have a database table called Lesson:
columns: [LessonID, LessonNumber, Description] ...plus some other columns
I have another table called Lesson_ScoreBasedSelection:
columns: [LessonID,NextLessonID_1,NextLessonID_2,NextLessonID_3]
When a lesson is completed, its LessonID is looked up in the Lesson_ScoreBasedSelection table to get the three possible next lessons, each of which are associated with a particular range of scores. If the score was 0-33, the LessonID stored in NextLessonID_1 would be used. If the score was 34-66, the LessonID stored in NextLessonID_2 would be used, and so on.
I want to constrain all the columns in the Lesson_ScoreBasedSelection table with foreign keys referencing the LessonID column in the lesson table, since every value in the Lesson_ScoreBasedSelection table must have an entry in the LessonID column of the Lesson table. I also want cascade updates turned on, so that if a LessonID changes in the Lesson table, all references to it in the Lesson_ScoreBasedSelection table get updated.
This particular cascade update seems like a very straightforward, one-way update, but when I try to apply a foreign key constraint to each field in the Lesson_ScoreBasedSelection table referencing the LessonID field in the Lesson table, I get the error:
Introducing FOREIGN KEY constraint 'c_name' on table 'Lesson_ScoreBasedSelection' may cause cycles or multiple cascade paths.
Can anyone explain why I'm getting this error or how I can achieve the constraints and cascading updating I described?
You can't have more than one cascading RI link to a single table in any given linked table. Microsoft explains this:
You receive this error message because
in SQL Server, a table cannot appear
more than one time in a list of all
the cascading referential actions that
are started by either a DELETE or an
UPDATE statement. For example, the
tree of cascading referential actions
must only have one path to a
particular table on the cascading
referential actions tree.
Given the SQL Server constraint on this, why don't you solve this problem by creating a table with SelectionID (PK), LessonID, Next_LessonID, QualifyingScore as the columns. Use a constraint to ensure LessonID and QualifyingScore are unique.
In the QualifyingScore column, I'd use a tinyint, and make it 0, 1, or 2. That, or you could do a QualifyingMinScore and QualifyingMaxScore column so you could say,
SELECT * FROM NextLesson
WHERE LessonID = #MyLesson
AND QualifyingMinScore <= #MyScore
AND #MyScore <= QualifyingMaxScore
Cheers,
Eric