Contents
Can dimension tables have foreign keys?
Dimension tables have a surrogate ID column that is the primary key of that dimension. A fact table may use these dimension surrogate IDs as foreign keys to the dimension table.
What are data warehouse constraints?
Why Constraints are Useful in a Data Warehouse Data cleanliness: Constraints can be used to verify that the data in the data warehouse conforms to basic level of data consistency and correctness. Thus, constraints are often used in a data warehouse to prevent the introduction of dirty data.
What is the role of dimension tables in the dimensional model?
A Dimension Table is a table in a star schema of a data warehouse. Data warehouses are built using dimensional data models which consist of fact and dimension tables. Dimension tables are used to describe dimensions; they contain dimension keys, values and attributes.
Why do we need a FOREIGN KEY constraint?
The reason for using a foreign key constraint in a data warehouse is the same as for any other database: to ensure data integrity. It is also possible that query performance will benefit because foreign keys permit certain types of query rewrite that are not normally possible without them.
When do you need a foreign key for a DW?
Foreign keys are a mechanism to preserve integrity constraints during database modifications. If your DW is read-only (accumulating data sources without writing back), there is no need for FK’s.
Is it good to use foreign keys in a query?
It is also possible that query performance will benefit because foreign keys permit certain types of query rewrite that are not normally possible without them. Data integrity is still the main reason to use foreign keys however. Yes, as a best practice, implement the FK constraints on your fact tables.
Why do we have to use FK constraints in Excel?
Because extra inner joins to dimensions are guaranteed to produce one and only one row, so the optimizer can use these constraints very effectively to eliminate the need to look up into the table. Without FK constraints, these lookups may have to be done to eliminate facts where the dimension does not exist.