The way I understand it, in the context of relational databases, a database has referential integrity if all referenced attribute values exist. In other words, if a value of one attribute references a value of another attribute, then the referenced value must exist. However, I cannot find any clear definition of referential integrity constraints. What exactly is a referential integrity constraint?
Related
Apologies in advance if this is a silly question. I recently faced this question while revising for databases, so I wish to check if my understanding is correct.
I understand that participation constraint is referring to the number of instances of an entity that can participate in a relationship. (E.g. Total and Partial).
Referential integrity is also a constraint that is related to relationships in a table, stating that a foreign key must reference an existing primary key of another entity.
Based on what I have read, I feel that referential integrity constraint is more about ensuring data integrity with regards to foreign keys, while participation constraint is more about just describing the relationships between two entities.
However, I keep having the feeling that Total Participation and Referential Integrity have a huge similarity. For example, let's say we have two tables
Customer(CustID, CustName)
Order(OrderID, CustID, OrderDate).
As CustID in the Order table must match a valid CustID in the Customer table, there is a referential integrity constraint here. Am I right to say that Order is also totally participating with Customer in a relationship?
This might be a silly question pardon me if.
I recently faced this question:
Consider the relations R1(A,B,C) and R2(B,P,Q), where A,B,C,P,Q are sets
of attributes. The values of B in R1 must mandatorily exist in R2. This is
an example of
a foreign key constraint
logical data independence
a referential integrity constraint
a domain constraint
Answer: a referential integrity constraint
I cannot distinguish between referential integrity constraint & foreign key constraint
Why we are preferring Referential Integrity Constraint:
According to the reference[1], the referential integrity constraint is the state of a database in which all values of all foreign keys are valid.
In your example, the line “ The values of B in R1 must mandatorily exist in R2” indicates--the child table(R2) contains all values of B from the parent table(R1), means all values of B in R2 are valid -- resulting in Referential integrity constraint.
Again why we are not using foreign key constraint:
According to the reference[2], it is not necessary to always have foreign keys to ensure referential integrity constraints. There are other ways of ensuring the integrity constraint.
Back to your example, there is no mention about foreign keys or primary keys. The question only indicates the reference between two tables. Hence, it would be better to choose the referential integrity constraint instead of foreign key constraint.
References:
https://www.toolbox.com/tech/big-data/question/difference-between-foreign-key-and-refrential-integrity-constraint-091703/
https://www.mssqltips.com/sqlservertip/4242/sql-server-referential-integrity-without-foreign-keys/
I found the same definition for referential and relational integrity. Are they the same? I have researched the two terms separately but cannot find any good definitions.
Yes, they are the same thing. The term "Referential Integrity" is used much more though.
Referential Integrity relates to Foreign Keys in a Relational DB. For a table to exhibit Referential Integrity, the Foreign Key must either be null or reference an existing PK value in the related table.
Hi I've set up two very basic tables. One table will act as a look up, with an identity field as a primary key. The other table uses the look up ID as a foreign key.
I have created a relationship constraint so now I cannot delete from the look up if the foreign key is used in the "main" table.
However my issue is i can add a record with a foreign key that doesn't exist.
To my way of thinking this shouldn't be allowed, can anyone tell me what setting I need to use to enforce this and whether this is typical database design or not?
Thanks Dave
You way of thinking is correct. Good database design provides some way of enforcing what is called "Referential Integrity". This is simply a buzzword for the concept you have derived on your own. Namely that a foreign key should be rejected if it refers to a non existent row. For a general discussion of referential integrity, see the following Wikipedia article. It's short.
http://en.wikipedia.org/wiki/Referential_integrity
Some pprogrammers would like to enforce referential integrity inside their programs. In general, it's a much better plan to define a referential integrity constraint inside the database, and let the DBMS do the enforcement. It's easier, it's faster, and it's more effective.
The SQL Data Definition Language (DDL) provides a way to declare a foreign key constraint when you create a table. The syntax differs a little between different dialects of SQL, but it's basically the same idea in all of them. Here's a capsule summary.
http://www.w3schools.com/sql/sql_foreignkey.asp
The documentation for SQL Server should have a description of the referential integrity constraint under the CREATE TABLE command.
I have two tables 'Elements' and 'Lists'
Lists has a primary key and a list name.
Elements has data pertaining to an individual entry in the list.
Elements needs a column that holds which list the element is in.
I've read about SQL's foreign key constraint and figure that is the best way to link the tables, but I'm using SQLite which doesn't enforce the foerign key constraint.
Is there a point to declaring the foreign key constraint if there is no enforcement?
It's always good to do, even if your database doesn't enforce the constraint (old MySQL, for instance). The reasoning for this, is that someday, someone will try reading your schema (perhaps even yourself).
If you can't use the new version, you can still declare the constraint and enforce it with triggers. In either case, I wouldn't omit the notation. It's far too helpful.
Nowadays sqlite enforces foreign keys, download the new release.
A foreign key is a field (or fields)
that points to the primary key of
another table. The purpose of the
foreign key is to ensure referential
integrity of the data. In other words,
only values that are supposed to
appear in the database are permitted.
It only enforces the "business rule". If you require this from the business side, then yes, it is required.
Indexing will not be affected.
You can still create indexes as requred.
Have a look at Foreign Key
and
Wikipedia Foreign key