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Is it bad to have many foreign keys?
It is NOT a bad thing to have more tables and relationships. The only issue — and it usually is not one — has to do with the overhead of maintaining the indexes that are used in enforcing those relationships.
How many foreign keys should a table have?
A table can reference a maximum of 253 other tables and columns as foreign keys (outgoing references).
How many foreign keys do you need?
We recommend that a table contain no more than 253 FOREIGN KEY constraints, and that it be referenced by no more than 253 FOREIGN KEY constraints. Consider the cost of enforcing FOREIGN KEY constraints when you design your database and applications.
Why are foreign keys important?
The primary purpose of the foreign key constraint is to enforce referential integrity and improve performance, but there are additional benefits of including them in your database design. To better understand the concept of the foreign key, you must understand the different relationships found in a relational database.
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.
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.
Which is a characteristic of a foreign key?
Primary and foreign keys are fundamental characteristics of relational databases, as originally noted in E.F. Codd ’s paper, “ A Relational Model of Data for Large Shared Data Banks ”, published in 1970. The quote often repeated is, “The key, the whole key, and nothing but the key, so help me Codd.”
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.