Should fact table have foreign keys?

Should fact table have foreign keys?

The fact table also has a primary (composite) key that is a combination of these four foreign keys. As a rule, each foreign key of the fact table must have its counterpart in a dimension table. This means that every table in a dimensional database that expresses a many-to-many relationship is a fact table.

Can a foreign key be null in fact table?

Null-valued measurements behave gracefully in fact tables. However, nulls must be avoided in the fact table’s foreign keys because these nulls would automatically cause a referential integrity violation.

What is fact table with example?

Thus, the fact table consists of two types of columns. The foreign keys column allows joins with dimension tables, and the measures columns contain the data that is being analyzed. In this example, the customer ID column in the fact table is the foreign key that joins with the dimension table.

Are there foreign keys for the fact table?

As I understand both these dimension tables will have integer primary keys for better performance, and the fact table will have its own integer primary key and also store foreign key references to these dimension tables.

Why is primary key not required on fact table in?

You are never going to retrieve one record from that fact table referring its surrogate key (use Indexes instead). Neither you are going to use that surrogate key to join the fact with other tables. Such a surrogate key will be completely waste of space in the database.

Why are null FKS used in fact tables?

People who do this like this approach because they have an aversion to outer joins. People who use NULL FKs in fact tables usually have an aversion to people who have an version to outer joins. 😉 (in other words, this is a stylistic issue which can generate religious wars)

Can you leave the FK to some dimension tables as null?

You can leave the FK to some dimension tables as NULL if those dimensions are not known or not applicable. You just have to remember to use outer joins when you do your reporting query.