I'm setting up Postgres table to organize active store commissions in my company and I need to set a rule for preventing insert errors.
I've tried to create a table without constraints and set the rules inside a Python script. Although this solution works, It does not prevent me or others from messing around when trying to update my table.
create table my_store_commissions (
ID SERIAL PRIMARY KEY ,
STORE_ID INTEGER,
COMMISSION NUMERIC,
IS_ACTIVE BOOLEAN
);
insert into my_store_commissions
values (1,100,0.90, False),
(2,100,0.89, False),
(3,100,0.78, False),
(4,100,0.78, True),
-- This code should not run
insert into my_store_commissions
values (5,100, 0.90, True)
I need to be able to have more than one store_id with is_active = False but only one store_id with is_active = True.
What you want is a partial [unique] index. That is, a unique index with a filter:
create unique index unq_my_store_commissions_store_id_active
on my_store_commissions(store_id)
where is_active;
Note that these can be tricky to handle when switching the active store. You may need to deactivate the previous store before setting the new one.
Related
We have an application whose work flow involves submitting information to an outside group and then inputting the user's id number into the system.
For that reason we allow a set default value "00000000" to be put into the id field as a tentative value before the entry is approved and a permanent one is put in.
What I'm looking for is essentially a way to ensure that the column remains unique except for that one value.
What I'm basically looking for is a UNIQUE constraint, however instead of NULL being the blank option it being "00000000". I've considered doing it as part of a CHECK constraint, however that seems like it'd be a big performance hit. (Under the assumption that UNIQUE does some kind of indexing)
Use Filtered Index
as the Following:-
CREATE UNIQUE NONCLUSTERED INDEX idx_yourcolumn_notspecificvalue
ON YourTable(yourcolumn)
WHERE yourcolumn != "00000000";
Example:
-- Create Table
Create table Test (id int identity, code varchar (100))
-- Create Unique Filtered Index
CREATE UNIQUE NONCLUSTERED INDEX idx_MyCol_Filtered
ON Test(code)
WHERE code != '00000000';
-- Insert Dumy Data >> '00000000' is repeated and '0101' is once
insert into Test (code)
Values ('00000000'),
('00000000'),
('00000000'),
('0101')
select * from Test
The Result:
-- Now try inserting '0101' again
insert into Test (code) Values ('0101')
The Result:
For more details:
Create Filtered Indexes
Approving the user entry through work flow sound like very crucial business logic. I would like to suggest that generate random but unique (like time stamp) number and insert with new user entry. Keep additional column which differentiate ( flag) approved entries from unapproved entries. Once the user gets approval from work flow, update the id and flag.
I want to add another row in my existing table and I'm a bit hesitant if I'm doing the right thing because it might skew the database. I have my script below and would like to hear your thoughts about it.
I want to add another row for 'Jane' in the table, which will be 'SKATING" in the ACT column.
Table: [Emp_table].[ACT].[LIST_EMP]
My script is:
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
Will this do the trick?
Your statement looks ok. If the database has a problem with it (for example, due to a foreign key constraint violation), it will reject the statement.
If any of the fields in your table are numeric (and not varchar or char), just remove the quotes around the corresponding field. For example, if emp_cod and line_no are int, insert the following values instead:
('REG','EMP',45233,'2016-06-20 00:00:00:00',2,'SKATING','JANE')
Inserting records into a database has always been the most common reason why I've lost a lot of my hairs on my head!
SQL is great when it comes to SELECT or even UPDATEs but when it comes to INSERTs it's like someone from another planet came into the SQL standards commitee and managed to get their way of doing it implemented into the final SQL standard!
If your table does not have an automatic primary key that automatically gets generated on every insert, then you have to code it yourself to manage avoiding duplicates.
Start by writing a normal SELECT to see if the record(s) you're going to add don't already exist. But as Robert implied, your table may not have a primary key because it looks like a LOG table to me. So insert away!
If it does require to have a unique record everytime, then I strongly suggest you create a primary key for the table, either an auto generated one or a combination of your existing columns.
Assuming the first five combined columns make a unique key, this select will determine if your data you're inserting does not already exist...
SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND [EMP_COD] = wsEmpCod AND [DATE] = wsDate AND [LINE_NO] = wsLineno
The wsXXX declarations, you will have to replace them with direct values or have them DECLAREd earlier in your script.
If you ran this alone and recieved a value of 1 or more, then the data exists already in your table, at least those 5 first columns. A true duplicate test will require you to test EVERY column in your table, but it should give you an idea.
In the INSERT, to do it all as one statement, you can do this ...
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
WHERE (SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND
[EMP_COD] = wsEmpCod AND [DATE] = wsDate AND
[LINE_NO] = wsLineno) = 0
Just replace the wsXXX variables with the values you want to insert.
I hope that made sense.
We are working on a database to store some evaluations we conduct. There are a few different types of evaluations and some have changed over time. Because of this we need to keep a record of exactly what an evaluation looked like when it was undertaken.
I figured that the best way to support this would be through a template style system.
With:
A table saving all possible options;
A table mapping options to a template;
An evaluations table mapping a participant to a template on a date/time; and
A table mapping evaluator comments to an option of an evaluation.
This is a skeleton for the design:
CREATE TABLE options (
id SERIAL PRIMARY KEY,
option TEXT NOT NULL
);
CREATE TABLE templates (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL
);
CREATE TABLE template_options (
template INTEGER NOT NULL REFERENCES templates( id ),
option INTEGER NOT NULL REFERENCES options( id ),
UNIQUE ( template, option )
);
CREATE TABLE participants (
id SERIAL PRIMARY KEY,
name TEXT NOT NULL
);
CREATE TABLE evaluations (
id SERIAL PRIMARY KEY,
template INTEGER NOT NULL REFERENCES templates( id ),
participant INTEGER NOT NULL REFERENCES participants( id ),
date TIMESTAMP WITH TIME ZONE NOT NULL
);
CREATE TABLE evaluation_data (
template INTEGER NOT NULL REFERENCES templates( id ),
option INTEGER NOT NULL REFERENCES options( id ),
evaluator_comments TEXT NOT NULL,
);
The design is able to capture our data but doesn't restrict the options saved in evaluation_data to the subset specified in the evaluation's template's option mapping. We could probably enforce it with a trigger (we can definitely do it with application logic [we are doing so at the moment]) but are we going down the wrong path with this design?
Can anybody think of a better way to do it?
Edit:
Added an example of a potential trigger we would need to use to ensure valid options are enforced with this design.
CREATE FUNCTION valid_option() RETURNS trigger as $valid_option$
BEGIN
IF NOT NEW.option IN ( SELECT template_options.option
FROM template_options
INNER JOIN templates
ON template_options.template = templates.id
WHERE templates.id = ( SELECT evaluations.template
FROM evaluations
WHERE evaluations.id = NEW.evaluation ) ) THEN
RAISE EXCEPTION 'This option is not mapped for this evaluations template.';
END IF;
RETURN NEW;
END
$valid_option$ LANGUAGE plpgsql;
CREATE TRIGGER valid_option BEFORE INSERT ON evaluation_data FOR EACH ROW EXECUTE PROCEDURE valid_option();
Remember that you need two sets of tables. The first set containing the assessment, questions, answer alternatives, categories(?) needed to display the assessment to the participant. The second set of tables to record data about the evaluation (ie. the participant taking the assessment): which assessment, which questions, which answer alternatives and in which order they were presented, which answer they entered (are they allowed to answer the same question multiple times?), etc.
We're using the following structure (I've removed topic scoring since you didn't ask about it):
Models for presenting an assessment:
Assessment: assessment_name, passing_status, version
Question: assessment, question_number, question_type, question_text
AnswerAlternative: question, correct?, answer_text, points
Models for recording an evaluation (participant taking an assessment):
Progress: started_timestamp, finished_timestamp, last_activity, status (includes "finished")
Result: user, assessment, progress, currently_active, score, passing_grade?
Answer: result, question, selected_answer_alternative, answer_text, score
To achieve your goal, I would augment this by writing the generated evaluation to a table and pointing to it from Reault. You could also record the selection and presentation criteria so you can re-generate the assessment programmatically (ie. if you're selecting the questions from a larger question db and re-ordering the answer alternatives before presenting them to the participant).
I have a table, something like:
create table state {foo int not null, bar int not null, baz varchar(32)};
create unique index on state(foo,bar);
I'd like to lock for a unique record in this table. However, if there's no existing record I'd like to prevent anyone else from inserting a record, but without inserting myself.
I'd use "FOR UPDATE WITH RS USE AND KEEP EXCLUSIVE LOCKS" but that only seems to work if the record exists.
A) You can let DB2 create every ID number. Let's say you have defined your Customer table
CREATE TABLE Customers
( CustomerID Int NOT NULL
GENERATED ALWAYS AS IDENTITY
PRIMARY KEY
, Name Varchar(50)
, Billing_Type Char(1)
, Balance Dec(9,2) NOT NULL DEFAULT
);
Insert rows without specifying the CustomerID, since DB2 will always produce the value for you.
INSERT INTO Customers
(Name, Billing_Type)
VALUES
(:cname, :billtype);
If you need to know what the last value assigned in your session was, you can then use the IDENTITY_VAL_LOCAL() function.
B) In my environment, I generally specify GENERATED BY DEFAULT. This is in part due to the nature of our principle programming language, ILE RPG-IV, where developers have traditionally to allowed the compiler to use the entire record definition. This leads me to I can tell everyone to use a sequence to generate ID values for a given table or set of tables.
You can grant select to only you, but if there are others with secadm or other privileges, they could insert.
You can do something with a trigger, something like check the current session, and if the user is your user, then it inserts the row.
if (SESSION_USER <> 'Alex) then
rollback -- or generate an exception
end if;
It seems that you also want to keep just one row, then, you can control that also in a trigger:
select count(0) into value from state
if (value > 1) then
rollback -- or generate an exception
end if;
I have a table with a column which contains a 'valid until' Date and I want to make sure that this can only be set to null in a single row within the table. Is there an easy way to do this?
My table looks like this (postgres):
CREATE TABLE 123.myTable(
some_id integer NOT NULL,
valid_from timestamp without time zone NOT NULL DEFAULT now(),
valid_until timestamp without time zone,
someString character varying)
some_id and valid_from is my PK. I want nobody to enter a line with a null value in column valid_until if there is already a line with null for this PK.
Thank you
In PostgreSQL, you have two basic approaches.
Use 'infinity' instead of null. Then your unique constraint works as expected. Or if you cannot do that:
CREATE UNIQUE INDEX null_valid_from ON mytable(someid) where valid_until IS NULL
I have used both approaches. I find usually the first approach is cleaner and it allows you to use range types and exclude constraints in newer versions of PostgreSQL better (to ensure no two time ranges overlap based on a given given someid), bt the second approach often is useful where the first cannot be done.
Depending on the database, you can't have null in a primary key (I don't know about all databases, but in sql server you can't). The easiest way around this I can think of is to set the date time to the minimum value, and then add a unique constraint on it, or set it to be the primary key.
I suppose another way would be to set up a trigger to check the other values in the table to see if another entry is null, and if there is one, don't allow the insert.
As Kevin said in his answer, you can set up a database trigger to stop someone from inserting more than one row where the valid until date is NULL.
The SQL statement that checks for this condition is:
SELECT COUNT(*)
FROM TABLE
WHERE valid until IS NULL;
If the count is not equal to 1, then your table has a problem.
The process that adds a row to this table has to perform the following:
Find the row where the valid until value is NULL
Update the valid until value to the current date, or some other meaningful date
Insert the new row with the valid until value set to NULL
I'm assuming you are Storing Effective-dated-records and are also using a valid from date.
If so, You could use CRUD stored procedures to enforce this compliance. E.G the insert closes off any null valid dates before inserting a new record with a null valid date.
You probably need other stored procedure validation to avoid overlapping records and to allow deleting and editing records. It may be more efficient (in terms of where clauses / faster queries) to use a date far in the future rather than using null.
I know only Oracle in sufficient detail, but the same might work in other databases:
create another column which always contains a fixed value (say '0') include this column in your unique key.
Don't use NULL but a specific very high or low value. I many cases this is actually easier to use then a NULL value
Make a function based unique key on a function converting the date including the null value to some other value (e.g. a string representation for dates and 'x' for null)
make a materialized view which gets updated on every change on your main table and put a constraint on that view.
select count(*) cnt from table where valid_until is NULL
might work as the select statement. And a check constraint limiting the cnt value to the values 0 and 1
I would suggest inserting to that table through an SP and putting your constraint in there, as triggers are quite hidden and will likely be forgotten about. If that's not an option, the following trigger will work:
CREATE TABLE dbo.TESTTRIGGER
(
YourDate Date NULL
)
CREATE TRIGGER DupNullDates
ON dbo.TESTTRIGGER
FOR INSERT, UPDATE
AS
DECLARE #nullCount int
SELECT #nullCount = (SELECT COUNT(*) FROM TESTTRIGGER WHERE YourDate IS NULL)
IF(#NullCount > 1)
BEGIN
RAISERROR('Cannot have Multiple Nulls', 16, 1)
ROLLBACK TRAN
END
GO
Well if you use MS SQL you can just add a unique Index on that column. That will allow only one NULL. I guess that if you use other RDBMS, this will still function.