I have a table like:
CREATE TABLE test(
id integer not null default nextval('test_id_seq'::regclass),
client_name_id integer not null
);
Foreign-key constraints:
"test_client_name_id_fkey" FOREIGN KEY (client_name_id) REFERENCES company(id) DEFERRABLE INITIALLY DEFERRED
and company table:
CREATE TABLE company(
id integer not null default nextval('company_id_seq'::regclass),
company_name character varying(64) not null
)
Now I have trigger on test table which fetch id from company table using provided value client_name_id which is string by matching it with company_name. but when I insert record PostgreSQL return error that client_name_id is string and int required which is true.
How can I tell PostgreSQL not to verify inserted row as I have taken care of it in my triggers.
What you are trying to do is very unorthodox. Are you sure, this is what you want? Of course, you cant enter a string (with non-digits) into an integer column. No surprise there, right? If you want to enter the text instead, you'd have to add a text column instead - with a fk-constraint to company(company_name) if you want to match your current layout.
ALTER TABLE test ALTER DROP COLUMN client_name_id; -- drops fk constraint, too
ALTER TABLE test ADD COLUMN client_name REFERENCES company(company_name);
You would need a UNIQUE constraint on company.company_name to allow this.
However, I would advise to rethink your approach. Your table layout seems proper as it is. The trigger is the unconventional element. Normally, you would reference the primary key, just like you have it now. No trigger needed. To get the company name, you would join the table in a SELECT:
SELECT *
FROM test t
JOIN company c ON t.client_name_id = c.id;
Also, these non-standard modifiers should only be there if you need them: DEFERRABLE INITIALLY DEFERRED. Like, when you have to enter values in table test before you enter the referenced values in table company (in the same transaction).
Related
Using PostgreSQL 9.2.4, I have a table users with a 1:many relation to the table user_roles. The users table stores both employees and other kinds of users.
Table "public.users"
Column | Type | Modifiers
-----------------+-------------------+-----------------------------------------------------
uid | integer | not null default nextval('users_uid_seq'::regclass)
employee_number | character varying |
name | character varying |
Indexes:
"users_pkey" PRIMARY KEY, btree (uid)
Referenced by:
TABLE "user_roles" CONSTRAINT "user_roles_uid_fkey" FOREIGN KEY (uid) REFERENCES users(uid)
Table "public.user_roles"
Column | Type | Modifiers
-----------+-------------------+------------------------------------------------------------------
id | integer | not null default nextval('user_roles_id_seq'::regclass)
uid | integer |
role | character varying | not null
Indexes:
"user_roles_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"user_roles_uid_fkey" FOREIGN KEY (uid) REFERENCES users(uid)
I want to ensure that the column users.employee_number cannot be NULL if there is a related row where user_roles.role_name contains an employee role name. That is, I want the database to enforce the constraint that for some roles, users.employee_number must have a value, but not for others.
How can I accomplish this, preferably without user-defined functions or triggers? I found (blog post, SO Answer) that SQL Server supports indexed views, which sounds like it would serve my purpose. However, I assume that materialized views will not work in my case, since they are not dynamically updated.
Clarifications
The formulation of this requirement leaves room for interpretation:
where UserRole.role_name contains an employee role name.
My interpretation:
with an entry in UserRole that has role_name = 'employee'.
Your naming convention is was problematic (updated now). User is a reserved word in standard SQL and Postgres. It's illegal as identifier unless double-quoted - which would be ill-advised. User legal names so you don't have to double-quote.
I am using trouble-free identifiers in my implementation.
The problem
FOREIGN KEY and CHECK constraint are the proven, air-tight tools to enforce relational integrity. Triggers are powerful, useful and versatile features but more sophisticated, less strict and with more room for design errors and corner cases.
Your case is difficult because a FK constraint seems impossible at first: it requires a PRIMARY KEY or UNIQUE constraint to reference - neither allows NULL values. There are no partial FK constraints, the only escape from strict referential integrity are NULL values in the referencing columns due to the default MATCH SIMPLE behavior of FK constraints. Per documentation:
MATCH SIMPLE allows any of the foreign key columns to be null; if any
of them are null, the row is not required to have a match in the referenced table.
Related answer on dba.SE with more:
Two-column foreign key constraint only when third column is NOT NULL
The workaround is to introduce a boolean flag is_employee to mark employees on both sides, defined NOT NULL in users, but allowed to be NULL in user_role:
Solution
This enforces your requirements exactly, while keeping noise and overhead to a minimum:
CREATE TABLE users (
users_id serial PRIMARY KEY
, employee_nr int
, is_employee bool NOT NULL DEFAULT false
, CONSTRAINT role_employee CHECK (employee_nr IS NOT NULL = is_employee)
, UNIQUE (is_employee, users_id) -- required for FK (otherwise redundant)
);
CREATE TABLE user_role (
user_role_id serial PRIMARY KEY
, users_id int NOT NULL REFERENCES users
, role_name text NOT NULL
, is_employee bool CHECK(is_employee)
, CONSTRAINT role_employee
CHECK (role_name <> 'employee' OR is_employee IS TRUE)
, CONSTRAINT role_employee_requires_employee_nr_fk
FOREIGN KEY (is_employee, users_id) REFERENCES users(is_employee, users_id)
);
That's all.
These triggers are optional but recommended for convenience to set the added tags is_employee automatically and you don't have to do anything extra:
-- users
CREATE OR REPLACE FUNCTION trg_users_insup_bef()
RETURNS trigger AS
$func$
BEGIN
NEW.is_employee = (NEW.employee_nr IS NOT NULL);
RETURN NEW;
END
$func$ LANGUAGE plpgsql;
CREATE TRIGGER insup_bef
BEFORE INSERT OR UPDATE OF employee_nr ON users
FOR EACH ROW
EXECUTE PROCEDURE trg_users_insup_bef();
-- user_role
CREATE OR REPLACE FUNCTION trg_user_role_insup_bef()
RETURNS trigger AS
$func$
BEGIN
NEW.is_employee = true;
RETURN NEW;
END
$func$ LANGUAGE plpgsql;
CREATE TRIGGER insup_bef
BEFORE INSERT OR UPDATE OF role_name ON user_role
FOR EACH ROW
WHEN (NEW.role_name = 'employee')
EXECUTE PROCEDURE trg_user_role_insup_bef();
Again, no-nonsense, optimized and only called when needed.
SQL Fiddle demo for Postgres 9.3. Should work with Postgres 9.1+.
Major points
Now, if we want to set user_role.role_name = 'employee', then there has to be a matching user.employee_nr first.
You can still add an employee_nr to any user, and you can (then) still tag any user_role with is_employee, irregardless of the actual role_name. Easy to disallow if you need to, but this implementation does not introduce any more restrictions than required.
users.is_employee can only be true or false and is forced to reflect the existence of an employee_nr by the CHECK constraint. The trigger keeps the column in sync automatically. You could allow false additionally for other purposes with only minor updates to the design.
The rules for user_role.is_employee are slightly different: it must be true if role_name = 'employee'. Enforced by a CHECK constraint and set automatically by the trigger again. But it's allowed to change role_name to something else and still keep is_employee. Nobody said a user with an employee_nr is required to have an according entry in user_role, just the other way round! Again, easy to enforce additionally if needed.
If there are other triggers that could interfere, consider this:
How To Avoid Looping Trigger Calls In PostgreSQL 9.2.1
But we need not worry that rules might be violated because the above triggers are only for convenience. The rules per se are enforce with CHECK and FK constraints, which allow no exceptions.
Aside: I put the column is_employee first in the constraint UNIQUE (is_employee, users_id) for a reason. users_id is already covered in the PK, so it can take second place here:
DB associative entities and indexing
First, you can solve this using a trigger.
But, I think you can solve this using constraints, with just a little weirdness:
create table UserRoles (
UserRoleId int not null primary key,
. . .
NeedsEmployeeNumber boolean not null,
. . .
);
create table Users (
. . .
UserRoleId int,
NeedsEmployeeNumber boolean,
EmployeeNumber,
foreign key (UserRoleId, NeedsEmployeeNumber) references UserRoles(UserRoleId, NeedsEmployeeNumber),
check ((NeedsEmployeeNumber and EmployeeNumber is not null) or
(not NeedsEmployeeNumber and EmployeeNumber is null)
)
);
This should work, but it is an awkward solution:
When you add a role to an employee, you need to add the flag along with the role.
If a role is updated to change the flag, then this needs to be propagated to existing records -- and the propagation cannot be automatic because you also need to potentially set EmployeeNumber.
New Answer:
This( SQL Sub queries in check constraint ) seems to answer your question, and the language is still in the 9.4 documentation( http://www.postgresql.org/docs/9.4/interactive/sql-createtable.html ).
Old Answer:
SELECT
User.*
, UserRole1.*
FROM
User
LEFT JOIN UserRole UserRole1
ON User.id = UserRole1.UserId
AND (
(
User.employee_number IS NOT NULL AND UserRole1.role_name IN (enumerate employee role names here)
)
OR
(User.employee_number IS NULL)
)
The above query selects all fields from User and all fields from UserRole(aliased as UserRole1). I assumed that the key field between the two fields is known as User.id and UserRole1.UserId, please change these to whatever the real values are.
In the JOIN part of the query there is an OR that on the left side requires an employee number not be NULL in the user table and that UserRole1.role_name be in a list that you must supply to the IN () operator.
The right part of the JOIN is the opposite, it requires that User.employee_number be NULL(this should be your non-employee set).
If you require a more exact solution then please provide more details on your table structures and what roles must be selected for employees.
I have three tables in a postgresql database, namely tec_configurations, tep_cores and tep2tec_bindings. The table tec2tep_bindings references to the primary key fields of the first two tables. The related create statements per table are listed in below sql snippets 2,3 and 4. I get the error indicated in the 1st snippet below. Could you please tell me how I can fix this error? The 'id' field in table TEC_CONFIGURATIONS is already unique since it is a primary key. So, I don't see a reason to get this error message.
SNIPPET 1 (Error message):
ERROR: there is no unique constraint matching given keys for referenced table
"tec_configurations"
SNIPPET 2 (TABLE tec_configurations):
CREATE TABLE IF NOT EXISTS TEC_CONFIGURATIONS (
ID SERIAL PRIMARY KEY,
TEC_ID INT NOT NULL,
HANDLER_MAC TEXT NOT NULL,
PRIMARY_MAC TEXT,
SECONDARY_MAC TEXT,
TERTIARY_MAC TEXT,
EXPECTED_FLOWS INT DEFAULT 0,
VERSION INT DEFAULT 0,
UUID TEXT DEFAULT NULL );
SNIPPET 3 (TABLE tep_cores):
CREATE TABLE IF NOT EXISTS TEP_CORES (
ID SERIAL PRIMARY KEY,
MAC TEXT,
UUID TEXT,
CORE_NO INT DEFAULT 0);
SNIPPET 4 (TABLE tec2tep_bindings)
CREATE TABLE IF NOT EXISTS TEC2TEP_BINDINGS (
ID SERIAL PRIMARY KEY,
TEC_ID_FK INT NOT NULL REFERENCES TEC_CONFIGURATIONS(ID),
TEP_CORE_ID_FK INT NOT NULL REFERENCES TEP_CORES(ID),
REPLICA_RANK INT DEFAULT 0);
Wild guess, since you're issuing create table if not exists rather than create table: one of the tables exists without the needed unique key (e.g. from lack of a primary key).
(If correct, I'd add this note. Some Postgres core devs were hostile to the idea of adding if exists and if not exists constructs, objecting thus: "What is supposed to happen when you create table if not exists, silently "succeed", and the existing table has a schema different from the one you were hoping for?")
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've got two tables - one is Product and one is ProductSearchResult.
Whenever someone tries to Insert a SearchResult with a product that is not listed in the Product table the foreign key constrain is violattet, hence i get an error.
I would like to know how i could get my database to automatically create that missing Product in the Product Table (Just the ProductID, all other attributes can be left blank)
Is there such thing as CASCADE ON INSERT? If there is, i was not able not get it working.
Rules are getting executed after the Insert, so because we get an Error beforehand there are useless if you USE an "DO ALSO". If you use "DO INSTEAD" and add the INSERT Command at the End you end up with endless recursion.
I reckon a Trigger is the way to go - but all my attempts to write one failed.
Any recommendations?
The Table Structure:
CREATE TABLE Product (
ID char(10) PRIMARY KEY,
Title varchar(150),
Manufacturer varchar(80),
Category smallint,
FOREIGN KEY(Category) REFERENCES Category(ID) ON DELETE CASCADE);
CREATE TABLE ProductSearchResult (
SearchTermID smallint NOT NULL,
ProductID char(10) NOT NULL,
DateFirstListed date NOT NULL DEFAULT current_date,
DateLastListed date NOT NULL DEFAULT current_date,
PRIMARY KEY (SearchTermID,ProductID),
FOREIGN KEY (SearchTermID) REFERENCES SearchTerm(ID) ON DELETE CASCADE,
FOREIGN KEY (ProductID) REFERENCES Product ON DELETE CASCADE);
Yes, triggers are the way to go. But before you can start to use triggers in plpgsql, you
have to enable the language. As user postgres, run the command createlang with the proper parameters.
Once you've done that, you have to
Write function in plpgsql
create a trigger to invoke that function
See example 39-3 for a basic example.
Note that a function body in Postgres is a string, with a special quoting mechanism: 2 dollar signs with an optional word in between them, as the quotes. (The word allows you to quote other similar quotes.)
Also note that you can reuse a trigger procedure for multiple tables, as long as they have the columns your procedure uses.
So the function has to
check if the value of NEW.ProductID exists in the ProductSearchResult table, with a select statement (you ought to be able to use SELECT count(*) ... INTO someint, or SELECT EXISTS(...) INTO somebool)
if not, insert a new row in that table
If you still get stuck, come back here.
In any case (rules OR triggers) the insert needs to create a new key (and new values for the attributes) in the products table. In most cases, this implies that a (serial,sequence) surrogate primary key should be used in the products table, and that the "real world" product_id ("product number") should default to NULL, and be degraded to a candidate key.
BTW: a rule can be used, rules just are tricky to implement correctly for N:1 relations (they need the same kind of EXISTS-logic as in Bart's answer above).
Maybe cascading on INSERT is not such a good idea after all. What do you want to happen if someone inserts a ProductSearchResult record for a not-existing product? [IMO a FK is always a domain; you cannot just extend a domain just by referring to a not-existant value for it; that would make the FK constraint meaningless]
I am trying to add a foreign key to a table, and it give me the following error:
There are no primary or candidate keys in the referenced table 'tbl_Person' that match the referencing column list in the foreign key 'P_ID'.
I have a tbl_Person, which is defined as:
P_ID INT (Primary Key)
f_Name,
l_Name
the other table is a comments table which is defined as:
C_ID INT,
Comments,
P_ID (should be the foreign key)
Trying to make a one to many relationship table, so when the user add a comment, it is referenced back to him, also, he can add onto the comments without initializing a new comment. Hopefully that makes a little sense.
Ex: Randy Bing enter "I love SQL", his ID is 1, f_Name is Randy, l_Name is Bing, his comments are "I love Sql". His comments should store a unique ID, as well as import his P_ID.
Later on when Randy wants to add onto the comment with the same C_ID where P_ID matches him without creating a new C_ID.
Here is the Code:
ALTER TABLE tbl_Comments
ADD CONSTRAINT P_ID
FOREIGN KEY (P_ID)
REFERENCES tbl_Person(P_ID)
Am I close to being on the right track?
This error usually means the datatypes are different between "Comments" and "Person", assuming this is the actual message
The SQL should be this
ALTER TABLE tbl_Comments WITH CHECK ADD
CONSTRAINT FK_Comments_Person FOREIGN KEY (P_ID) REFERENCES tbl_Person (P_ID)
This matches what you added. So:
check datatypes are both int
ensure P_ID is primary key on tbl_Person
(Edit, Dec 2011) collation and length must be the same for varchar columns too
In Object Explorer, connect to an instance of Database Engine.
On the Standard bar, click New Query.
The example creates a foreign key on the column TempID and references the column SalesReasonID in the Sales.SalesReason table.
USE AdventureWorks2012;
GO
ALTER TABLE Sales.TempSalesReason
ADD CONSTRAINT FK_TempSales_SalesReason FOREIGN KEY (TempID)
REFERENCES Sales.SalesReason (SalesReasonID)
ON DELETE CASCADE
ON UPDATE CASCADE
;
GO
the name of your constraint, p_id,
clashes with the name of the p_id column