I have searched for solution to my problem and this question describes it perfectly.
Let´s say I have one table called ProjectTimeSpan (which I haven´t, just as example!) containing the columns StartDate and EndDate.
And that I have another table called SubProjectTimeSpan, also containing columns called StartDate and EndDate, where I would like to set a Check constraint that makes it impossible to set StartDate and EndDate to values "outside" the ProjectTimeSpan.StartDate to ProjectTimeSpan.EndDate
Kind of a Check constraint that knows about another tables values...
Is this possible?
But I have a hard time to implement the solution to oracle. I've got even more puzzled when other articles stated that check constraint can not relate to other tables.
No it can't.
A FOREIGN KEY constraint can (and must) relate to another table, but it can only perform equiality checks.
I.e. you can test that a column (or a set of columns) are equal to those in the other table but not more complex conditions (like inside a span or whatever).
You'll have to implement a trigger for that.
Related
I fail to understand the logic of the unique constraint when it's based on 2 fields.
I have the following table named DESCRIPTIONS including 3 columns: ID_DESCRIPTION, NAME, ID_DESCRIPTION_TYPE
Now ID_DESCRIPTION is the primary key, and there is a unique constraint UK_DESCRIPTION on couple (ID_DESCRIPTION, NAME).
If I try to run the following query:
UPDATE DESCRIPTIONS SET NAME = 'USA' WHERE ID_DESCRIPTION = 9255813
I'm getting an ORA-00001 exception, saying that unique constraint UK_DESCRIPTION is violated.
Now this would mean that the couple (9255813,'USA') already exists right ?
However, I don't see how this is possible since the ID_DESCRIPTION is a primary key and therefore unique AND the results of the query
SELECT * FROM DESCRIPTIONS WHERE ID_DESCRIPTION = 9255813
only return 1 result, the one I want to update.
What am I failing to understand here ?
I am going to guess that uk_description is in fact a unique key based on the single column of NAME.
"It is unfortunately not."
Okay, the other explanation is that it is a multi-column key based on a different set of columns from what you think. (NAME, ID_DESCRIPTION_TYPE) would also fit the described behaviour.
To be fair, a unique key on(NAME, ID_DESCRIPTION_TYPE) makes more sense. For example, this is the key you'd want when the table is a single reference data look-up (which is a horrible model but common enough). Whereas a compound key of ID_DESCRIPTION, NAME) would do nothing but undermine the primary key.
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I have a situation i can't find an explanation for, here it is. (I'll use hypothetical info since the original are really big.)
I have a table, let's say:
table_a
-------------
name
last name
dept
status
notes
And this table has a trigger on insert, which does a lot of validation to the info to change the status field of the new record according to the results of the validation, some of the validations are:
- check for the name existing in a dictionary
- check for the last name existing in a dictionary
- check that fields (name,last name,dept) aren't already inserted in table_b
- ... and so on
The thing is, if I do an insert on the table via query, like
insert into table_a
(name,last_name,dept,status,notes)
values
('john','smith',1,0,'new');
it takes only 173 ms to do all the validation process, update the status field and insert the record in the table. (the validation process does all the searches via indexes)
But if I try this via SQLloader, reading a file with 5000 records, it takes like 40 minutes to validate and insert 149 records (of course i killed it...)
So I tried loading the data disabling the trigger (to check speed)
and I got that it loads like all the records in less than 10 seconds.
So my question is, what can I do to improve this process? My only theory is that I could be saturating the database because it loads so fast and launches many instances of the trigger, but I really don't know.
My objective is to load around 60 files with info and validate them through the process in the trigger (willing to try other options though).
I would really appreciatte any help you can provide!!
COMPLEMENT---------------------------------------------------------------------------------
Thanks for the answer, now i'll read all about this, now hope you can help me with this part. let me explain some of the functionality i need (and i used a trigger cause i couldn't think of anything else)
so the table data comes with this (important) fields:
pid name lastname birthdate dept cicle notes
the data comes like this
name lastname birthdate dept
now, the trigger does this to the data:
Calls a function to calculate the pid (is calculated based on the name, lastname and birthdate with an algorithm)
Calls a function to check for the names on the dictionary (thats because in my dictionary i have single names, meaning if a person is named john aaron smith jones the function splits john aaron in two, and searches for john and aaron in the dictionary in separate querys, thats why i didn't use a foreign key [to avoid having lots of combinations john aaron,john alan,john pierce..etc]) --->kinda stuck on how to implement this one with keys without changing the dictionary...maybe with a CHECK?, the lastname foreign key would be good idea.
Gets the cicle from another table according to the dept and the current date (because a person can appear twice in the table in the same dept but in different cicle) --->how could i get this cicle value in a more efficient way to do the correct search?
And finally, after all this validation is done, i need to know exactly which validation wasn't met (thus the field notes) so the trigger concatenates all the strings of failed validations, like this:
lastname not in dictionary, cannot calculate pid (invalid date), name not in dictionary
i know that if the constraint check isn't met all i could do is insert the record in another table with the constraint-failed error message, but that only leaves me with one validation, am i right? but i need to validate all of them and send the report to other department so they can review the data and make all the necessary adjustments to it.
Anyway, this is my situation right now, i'll explore possibilities and hope you can share some light on the overall process, Thank you very much for your time.
You're halfway to the solution already:
"So I tried loading the data disabling the trigger (to check speed) ... it loads like all the records in less than 10 seconds."
This is not a surprise. Your current implementation executes a lot of single row SELECT statements for each row you insert into table B. That will inevitably give you a poor performance profile. SQL is a set-based language and performs better with multi-row operations.
So, what you need to do is find a way to replace all the SELECT statements which more efficient alternatives. Then you'll be able to drop the triggers permanently. For instance, replace the look-ups on the dictionary with foreign keys between the table A columns and the reference table. Relational integrity constraints, being internal Oracle code, perform much better than any code we can write (and work in multi-user environments too).
The rule about not inserting into table A if a combination of columns already exists in table B is more problematic. Not because it's hard to do but because it sounds like poor relational design. If you don't want to load records in table A when they already exits in table B why aren't you loading into table B directly? Or perhaps you have a sub-set of columns which should be extracted from table A and table B and formed into table C (which would have foreign key relationships with A and B)?
Anyway, leaving that to one side, you can do this with set-based SQL by replacing SQL*Loader with an external table. An external table allows us to present a CSV file to the database as if it were a regular table. This means we can use it in normal SQL statements. Find out more.
So, with foreign key constraints on dictionary and an external table you can replace teh SQL Loader code with this statement (subject to whatever other rules are subsumed into "...and so on"):
insert into table_a
select ext.*
from external_table ext
left outer join table_b b
on (ext.name = b.name and ext.last_name = b.last_name and ext.dept=b.dept)
where b.name is null
log errors into err_table_a ('load_fail') ;
This employs the DML error logging syntax to capture constraint errors for all rows in a set-based fashion. Find out more. It won't raise exceptions for rows which already exist in table B. You could either use the multi-table INSERT ALL to route rows into an overflow table or use a MINUS set operation after the event to find rows in the external table which aren't in table A. Depends on your end goal and how you need to report things.
Perhaps a more complex answer than you were expecting. Oracle SQL is a very extensive SQL implementation, with a lot of functionality for improving the efficient of bulk operations. It really pays us to read the Concepts Guide and the SQL Reference to find out just how much we can do with Oracle.
I have little problem with programming trigger for my dtb. I need to control 2 values in one 1 table. I have table called Concert and it has 2 foreign keys: 1 is the id of table Place. Second is not important for this I think.
Concert: id_concert, id_place<fk>, id_organizer<fk>, date, name, sponsor
Place: id_place, name, capacity, adress, town
What I want to eliminate is, that 2 concerts organized at same day cannot be on one place. So, I need to somehow control that user cannot insert the same date and same place for concert if there already concert with this values exists.
Thank you very much for your suggestions and sorry for bad english.
You need to add a unique constraint on your Concert table that consists of the (id_place, date) pair. This would instruct the database engine to not allow more than one Concert in the same place at the same time.
For Oracle, information can be found here: http://www.techonthenet.com/oracle/unique.php
CREATE TABLE Concert
(
... (filled in with your existing table definition)
CONSTRAINT concert_place_unique UNIQUE (id_place, date)
);
or to alter an existing table:
ALTER TABLE Concert
add CONSTRAINT concert_place_unique UNIQUE (id_place, date);
Constraints are the proper way to handle this condition, not triggers. Constraints are database intrinsic and have no race conditions and prevent the data from being added in the first place.
I have come into a bump at my current company where they have an account and a member. For some reason or another both are stored in separate tables.
Right now a member and an account can be registered. That's fine, except the users of both member and an account can have the same username. This is of course as you all know just wrong. Especially since they use the username to login to the same system except with different functionality levels.
Right now we are doing a check at the application level, and we're just wondering if it's possible to get the database to enforce two columns to be unique, say like a union of the two tables.
Can't set them up as primary or foreign key at the moment but that's for future anyway. Right now looking for a quick fix. In the future I will probably merge databases and get all members added on as new rows in the account table and add a boolean for IsMember.
In general, I agree with the consensus opinion that it's better to fix the design than to kluge a fix using triggers. However, a properly implemented trigger-based solution is still probably better than your current situation.
If you're going to use triggers, the right way to do it is to:
Create a new table that will contain nothing but usernames, with a primary key enforcing uniqueness (this may, in fact, be a good candidate for an indes-organized table).
Create before-insert triggers on both existing tables that add the new username to the new table. If the new username already exists, an error will be thrown, preventing the insert of both rows. Of course, the application will need to be able to handle this error gracefully (presumably it already can, for scenarios in which the new username already exists in the table it's being added to).
The wrong way to do this would be to make the trigger select from the other table, in order to verify uniqueness.
You can add a trigger that enforces your requirement.
The recommended triggers tend to be really brittle with concurrent transaction.
What you can do (AFAIK) is to create a materialized view containing the union of the column in question and put a unique constraint on that column.
Make sure you do some performance tests though.
As you use a soft delete pattern.
A trigger could be used (on each table) as a temporary measure.
By inserting a disabled record in the the other table, you will get a failure if the other record already exists
Remember this will not enforce the rule on existing data, only records that are inserted will be checked
Something like this:
-- Insert into the accounts table too
CREATE OR REPLACE TRIGGER tr_member_chk
BEFORE INSERT ON members
FOR EACH ROW
BEGIN
INSERT INTO account (name, id, etc, isenabled) VALUES(:new.name, :new.id, :new.etc, 0);
END;
-- Insert into the members table too
CREATE OR REPLACE TRIGGER tr_account_chk
BEFORE INSERT ON accounts
FOR EACH ROW
BEGIN
INSERT INTO members (name, id, etc,isenabled) VALUES(:new.name, :new.id, :new.etc,0);
END;
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.