What is composite key and surrogate key?
A composite key is simply a key that contains two or more columns. A surrogate key is one which is not naturally unique to the data but is added or imposed onto the data for (hopefully) a good reason. Examples can include IDENTITY columns in SQL Server – known as autonumbers sometimes in other products.
What is true about composite primary keys?
A composite key can be defined as the primary key. This is done using SQL statements at the time of table creation. It means that data in the entire table is defined and indexed on the set of columns defined as the primary key.
Which is better a surrogate key or composite key?
A surrogate key might seem like a tidier solution than a key based on more than one column, but they do not simplify data design – using an identity column over a composite key actually complicates the data design.
When to use identity column or surrogate key?
Using an identity column for tables that define entities is fair enough, but I’m not sure why you would use a surrogate key over a composite key for tables that relate entities. Firstly, it’s worth pointing out that an identity column is only a type of primary key.
Do you have to create composite key for identity column?
In order to guarantee data integrity you will have to add a constraint and an index onto the columns that would form the composite key as well as having to create an identity column and primary key. There are also a number of practical maintenance issues with identity columns which do make life more difficult in the long term:
Which is the composite key in a table?
Normally a table with have an id field as the primary key. By adding client_id the key is now composite key. And it is necessary to carry client_id to all child table. The composite key is based on 2 surrogate keys and is a bulletproof way to ensure data integrity among clients and within the database a whole.