I want to understand what does before update in trigger means.
I have a table called DEPT_MST where DEPT_ID is the primary key. It has 2 rows with DEPT_ID 1 and 2.
Another table EMP has columns EMP_ID as primary key and EMP_DEPT_ID which is a foreign key referencing DEPT_ID of DEPT table.
Now if I add before update trigger on EMP tables EMP_DEPT_ID column which will check if new value for EMP_DEPT_ID is present in master table DEPT if now then will insert new row with new DEPT_ID to DEPT table.
Now if I update EMP_DEPT_ID to 3 where EMP_DEPT_ID is 2 in EMP table it is giving integrity constraint violation error parent not found.
So,
Does this mean that Oracle checks for integrity constraints first and then calls the "before update" trigger?
Then how can we bypass this check and call before update trigger?
What exactly does "before update" mean here?
How can I achieve above result by using triggers and not by using explicit PL SQL block?
Thank you
Non-deferred foreign key constraints are evaluated before triggers are called, yes.
If you can declare the foreign key constraint to be deferrable (which would require dropping and re-creating it if the existing constraint is not deferrable)
ALTER TABLE emp
ADD CONSTRAINT fk_emp_dept (emp_dept_id) REFERENCES dept( dept_id )
INITIALLY DEFERRED DEFERRABLE;
In your application, you can then set the constraint to be deferrable, run your INSERT statement causing the trigger to fire and insert the parent row. Your foreign key constraint will be validated when the transaction commits.
An alternative to defining the constraint to be deferrable would be to rename the emp table to, say, emp_base, create a view named emp and then create an instead of insert trigger on emp that implements the logic of first inserting into dept and then inserting into emp_base.
Related
I created a table in PostgreSQL with a foreign key constraint.
I dropped the table to which the foreign key belongs. Now how to alter the table or how to defer the foreign key present in the table?
To clarify:
I have a table named test. It has a column called subjectName, which is a foreign key of subject Table. Now I dropped subject table. How to remove the FK constaint on table test
Assuming the following tables:
create table subject
(
name varchar(10) primary key
);
create table test
(
some_column integer,
subject_name varchar(10) not null references subject
);
there are two scenarios what could have happened when you dropped the table subject:
1. you didn't actually drop it:
drop table subject;
ERROR: cannot drop table subject because other objects depend on it
Detail: constraint test_subject_name_fkey on table test depends on table subject
Hint: Use DROP ... CASCADE to drop the dependent objects too.
2. you did drop it, then the foreign key is gone as well.
drop table subject cascade;
NOTICE: drop cascades to constraint test_subject_name_fkey on table test
which tells you that the foreign key constraint was automatically dropped.
Perhaps your question in not exactly what you mean. Are you wanting to remove the which was a foreign key from the table. As amply indicated if you dropped the parent table then the FK is also dropped. However the column itself is not dropped from the child table. To remove that you need to alter the table.
alter table test drop column subject_name;
See demo here
I have a column in db which has 5 columns but no primary key.
One of the columns is named myTable_id and is integer.
I want to check if the table has a primary key column. If it doesn't, then make myTable_id a primary key column and make it identity column. Is there a way to do this?
I tried with this:
ALTER TABLE Persons
DROP CONSTRAINT pk_PersonID
ALTER TABLE Persons
ADD PRIMARY KEY (P_Id)
and I get syntax error in Management studio.
This checks if primary key exists, if not it is created
IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE CONSTRAINT_TYPE = 'PRIMARY KEY' AND TABLE_NAME = 'Persons'
AND TABLE_SCHEMA ='dbo')
BEGIN
ALTER TABLE Persons ADD CONSTRAINT pk_PersonID PRIMARY KEY (P_Id)
END
ELSE
BEGIN
-- Key exists
END
fiddle: http://sqlfiddle.com/#!6/e165d/2
ALTER TABLE Persons
ADD CONSTRAINT pk_PersonID PRIMARY KEY (P_Id)
An IDENTITY constraint can't be added to an existing column, so how you add this needs to be your initial thought. There are two options:
Create a new table including a primary key with identity and drop the existing table
Create a new primary key column with identity and drop the existing 'P_ID' column
There is a third way, which is a better approach for very large tables via the ALTER TABLE...SWITCH statement. See Adding an IDENTITY to an existing column for an example of each. In answer to this question, if the table isn't too large, I recommend running the following:
-- Check that the table/column exist and no primary key is already on the table.
IF COL_LENGTH('PERSONS','P_ID') IS NOT NULL
AND NOT EXISTS (SELECT 1 FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
WHERE CONSTRAINT_TYPE = 'PRIMARY KEY' AND TABLE_NAME = 'PERSONS')
-- Add table schema to the WHERE clause above e.g. AND TABLE_SCHEMA ='dbo'
BEGIN
ALTER TABLE PERSONS
ADD P_ID_new int IDENTITY(1, 1)
GO
ALTER TABLE PERSONS
DROP COLUMN P_ID
GO
EXEC sp_rename 'PERSONS.P_ID_new', 'P_ID', 'Column'
GO
ALTER TABLE PERSONS
ADD CONSTRAINT PK_P_ID PRIMARY KEY CLUSTERED (P_ID)
GO
END
Notes:
By explicitly using the CONSTRAINT keyword the primary key constraint is given a particular name rather than depending on SQL Server to auto-assign a name.
Only include CLUSTERED on the PRIMARY KEY if the balance of searches for a particular P_ID and the amount of writing outweighs the benefits of clustering the table by some other index. See Create SQL IDENTITY as PRIMARY KEY.
You can check if primary key exists or not using OBJECTPROPERTY Transact SQL, use 'TableHasPrimaryKey' for the second arguments.
DECLARE #ISHASPRIMARYKEY INT;
SELECT #ISHASPRIMARYKEY = OBJECTPROPERTY(OBJECT_ID('PERSONS'), 'TABLEHASPRIMARYKEY');
IF #ISHASPRIMARYKEY IS NULL
BEGIN
-- generate identity column
ALTER TABLE PERSONS
DROP COLUMN P_ID;
ALTER TABLE PERSONS
ADD P_ID INT IDENTITY(1,1);
-- add primary key
ALTER TABLE PERSONS
ADD CONSTRAINT PK_PERSONID PRIMARY KEY (P_ID);
END;
I don't think you can do that. For making a column into an identity column I think you have to drop the table entirely.
I currently have a parent table:
CREATE TABLE members (
member_id SERIAL NOT NULL, UNIQUE, PRIMARY KEY
first_name varchar(20)
last_name varchar(20)
address address (composite type)
contact_numbers varchar(11)[3]
date_joined date
type varchar(5)
);
and two related tables:
CREATE TABLE basic_member (
activities varchar[3]) // can only have 3 max activites
INHERITS (members)
);
CREATE TABLE full_member (
activities varchar[]) // can 0 to many activities
INHERITS (members)
);
I also have another table:
CREATE TABLE planner (
day varchar(9) FOREIGN KEY REFERENCES days(day)
time varchar(5) FOREIGN KEY REFERENCES times(time)
activity varchar(20) FOREIGN KEY REFERENCES activities(activity)
member bigint FOREIGN KEY REFERENCES members(member_id)
);
ALTER TABLE planner ADD CONSTRAINT pk_planner PRIMARKY KEY (day,time,activity,member);
I am currently trying to add with
INSERT INTO planner VALUES ('monday','09:00','Weights',2);
I have added a set into full_members with
INSERT INTO full_members
VALUES (Default, 'Hayley', 'Sargent', (12,'Forest Road','Mansfield','Nottinghamshire','NG219DX'),'{01623485764,07789485763,01645586754}',20120418,'Full');
My insert into Planner is currently not working — can you explain why?
i managed ot answer my own question it was becuase at the moment posgreSQL doesn't work very well with inheritence and foreign keys, so i have ot create a rule
CREATE RULE member_ref
AS ON INSERT TO planner
WHERE new.member NOT IN (SELECT member_id FROM members)
DO INSTEAD NOTHING;
this is basically the same as a foreign key
Not sure if this will be better solution but here it goes...
The principle is quite simple:
create new table lets call it table_with_pkeys which will replicate primary key column(s) of inherited tables child1, child2, child3...
create triggers on inherited tables, after insert, insert new PK into table_with_pkeys newly created PK, after update if it changes update it and after delete delete the same PK from table_with_pkeys.
Then in every table which should reference child1, child2 or whichever through parent table's PK using FK, point that FK not to parent's PK, but to table_with_pkeys which has copies of all childs PK's, and so you will have easy manageable way to have foreign keys that can cascade updates, restrict updates and so on.
Hope it helps.
You are missing an open quote before the 12 in the address:
INSERT INTO full_members
VALUES (Default, 'Hayley', 'Sargent', (12 Forest Road', 'Mansfield', 'Nottinghamshire', 'NG219DX'),
'{01623485764,07789485763,01645586754}',20120418,'Full');
should be:
INSERT INTO full_members
VALUES (Default, 'Hayley', 'Sargent', ('12 Forest Road', 'Mansfield', 'Nottinghamshire', 'NG219DX'),
'{01623485764,07789485763,01645586754}',20120418,'Full');
If the materialized view approach doesn't work for you above, create constraint triggers to check the referential integrity. Unfortunately declarative referential integrity doesn't work well with inheritance at present.
This is the situation: I have two tables where the one references the other (say, table2 references table1). When creating these tables, I did set the foreign key constraint as DEFERRABLE and the ON UPDATE and ON DELETE clauses as NO ACTION (which is the default).
But still, when running the transaction below, I get the following error.
Transaction:
START TRANSACTION;
SET CONSTRAINTS ALL DEFERRED;
UPDATE table1 SET blah blah;
UPDATE table2 SET blah blah;
COMMIT;
Error:
ERROR: update or delete on table "table1" violates foreign key constraint "table1_column_fkey" on table "table2"
DETAIL: Key (column1)=(blahblah) is still referenced from table "table2".
And table construction:
CREATE TABLE table1(
column1 CHAR(10),
[...]
PRIMARY KEY (column1)
);
CREATE TABLE table2(
primkey CHAR(9),
[...]
column2 CHAR(10) NOT NULL,
PRIMARY KEY(primkey),
FOREIGN KEY(column2) REFERENCES table1(column1) DEFERRABLE
);
What I want to do is to defer the foreign key checking while the transaction is in progress, until it commits. I just can't see why is this error returning and how can I make the transaction work.
The problem was indeed a foreign key constraint violation. I mean, the constraints were indeed deferred within the transaction, but the problem was that at the end of the transaction, after table1 and table2 were updated, the new data were violating a foreign key constraint. I was updating the primary key of a table1 row, which was still being referenced by some table2 rows. These rows I had to update them too, so that the referencing column of table2 rows matched the updated primary key of table1's row. I changed the 'UPDATE' queries within the transaction and the problem got solved.
Sorry to put you into this. The solution was so simple, but that day I coudn't see it.
I've created some tables in postgres, added a foreign key from one table to another and set ON DELETE to CASCADE. Strangely enough, I have some fields that appear to be violating this constraint.
Is this normal behaviour? And if so, is there a way to get the behaviour I want (no violations possible)?
Edit:
I orginaly created the foreign key as part of CREATE TABLE, just using
... REFERENCES product (id) ON UPDATE CASCADE ON DELETE CASCADE
The current code pgAdmin3 gives is
ALTER TABLE cultivar
ADD CONSTRAINT cultivar_id_fkey FOREIGN KEY (id)
REFERENCES product (id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE;
Edit 2:
To Clarify, I have a sneaking suspicion that the constraints are only checked when updates/inserts happen but are then never looked at again. Unfortunately I don't know enough about postgres to find out if this is true or how fields could end up in the database without those checks being run.
If this is the case, is there some way to check all the foreign keys and fix those problems?
Edit 3:
A constraint violation can be caused by a faulty trigger, see below
I tried to create a simple example that shows foreign key constraint being enforced. With this example I prove I'm not allowed to enter data that violates the fk and I prove that if the fk is not in place during insert, and I enable the fk, the fk constraint throws an error telling me data violates the fk. So I'm not seeing how you have data in the table that violates a fk that is in place. I'm on 9.0, but this should not be different on 8.3. If you can show a working example that proves your issue that might help.
--CREATE TABLES--
CREATE TABLE parent
(
parent_id integer NOT NULL,
first_name character varying(50) NOT NULL,
CONSTRAINT pk_parent PRIMARY KEY (parent_id)
)
WITH (
OIDS=FALSE
);
ALTER TABLE parent OWNER TO postgres;
CREATE TABLE child
(
child_id integer NOT NULL,
parent_id integer NOT NULL,
first_name character varying(50) NOT NULL,
CONSTRAINT pk_child PRIMARY KEY (child_id),
CONSTRAINT fk1_child FOREIGN KEY (parent_id)
REFERENCES parent (parent_id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
)
WITH (
OIDS=FALSE
);
ALTER TABLE child OWNER TO postgres;
--CREATE TABLES--
--INSERT TEST DATA--
INSERT INTO parent(parent_id,first_name)
SELECT 1,'Daddy'
UNION
SELECT 2,'Mommy';
INSERT INTO child(child_id,parent_id,first_name)
SELECT 1,1,'Billy'
UNION
SELECT 2,1,'Jenny'
UNION
SELECT 3,1,'Kimmy'
UNION
SELECT 4,2,'Billy'
UNION
SELECT 5,2,'Jenny'
UNION
SELECT 6,2,'Kimmy';
--INSERT TEST DATA--
--SHOW THE DATA WE HAVE--
select parent.first_name,
child.first_name
from parent
inner join child
on child.parent_id = parent.parent_id
order by parent.first_name, child.first_name asc;
--SHOW THE DATA WE HAVE--
--DELETE PARENT WHO HAS CHILDREN--
BEGIN TRANSACTION;
delete from parent
where parent_id = 1;
--Check to see if any children that were linked to Daddy are still there?
--None there so the cascade delete worked.
select parent.first_name,
child.first_name
from parent
right outer join child
on child.parent_id = parent.parent_id
order by parent.first_name, child.first_name asc;
ROLLBACK TRANSACTION;
--TRY ALLOW NO REFERENTIAL DATA IN--
BEGIN TRANSACTION;
--Get rid of fk constraint so we can insert red headed step child
ALTER TABLE child DROP CONSTRAINT fk1_child;
INSERT INTO child(child_id,parent_id,first_name)
SELECT 7,99999,'Red Headed Step Child';
select parent.first_name,
child.first_name
from parent
right outer join child
on child.parent_id = parent.parent_id
order by parent.first_name, child.first_name asc;
--Will throw FK check violation because parent 99999 doesn't exist in parent table
ALTER TABLE child
ADD CONSTRAINT fk1_child FOREIGN KEY (parent_id)
REFERENCES parent (parent_id) MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE;
ROLLBACK TRANSACTION;
--TRY ALLOW NO REFERENTIAL DATA IN--
--DROP TABLE parent;
--DROP TABLE child;
Everything I've read so far seems to suggest that constraints are only checked when the data is inserted. (Or when the constraint is created) For example the manual on set constraints.
This makes sense and - if the database works properly - should be good enough. I'm still curious how I managed to circumvent this or if I just read the situation wrong and there was never a real constraint violation to begin with.
Either way, case closed :-/
------- UPDATE --------
There was definitely a constraint violation, caused by a faulty trigger. Here's a script to replicate:
-- Create master table
CREATE TABLE product
(
id INT NOT NULL PRIMARY KEY
);
-- Create second table, referencing the first
CREATE TABLE example
(
id int PRIMARY KEY REFERENCES product (id) ON DELETE CASCADE
);
-- Create a (broken) trigger function
--CREATE LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION delete_product()
RETURNS trigger AS
$BODY$
BEGIN
DELETE FROM product WHERE product.id = OLD.id;
-- This is an error!
RETURN null;
END;
$BODY$
LANGUAGE plpgsql;
-- Add it to the second table
CREATE TRIGGER example_delete
BEFORE DELETE
ON example
FOR EACH ROW
EXECUTE PROCEDURE delete_product();
-- Now lets add a row
INSERT INTO product (id) VALUES (1);
INSERT INTO example (id) VALUES (1);
-- And now lets delete the row
DELETE FROM example WHERE id = 1;
/*
Now if everything is working, this should return two columns:
(pid,eid)=(1,1). However, it returns only the example id, so
(pid,eid)=(0,1). This means the foreign key constraint on the
example table is violated.
*/
SELECT product.id AS pid, example.id AS eid FROM product FULL JOIN example ON product.id = example.id;