What is the difference between a composite key and a composite attribute?
Discuss the difference between a composite key and a composite attribute. How would each be indicated in an ERD? A composite key is one that consists of more than one attribute. A derived attribute is an attribute whose value is calculated (derived) from other attributes.
Can a unique key be a primary key?
A primary key must be unique. A unique key does not have to be the primary key – see candidate key. That is, there may be more than one combination of columns on a table that can uniquely identify a row – only one of these can be selected as the primary key.
Is it good to use composite primary keys?
Composite PRIMARY KEYs are often a very “good thing” and the only way to model natural situations that occur in everyday life! Having said that, there would also be many situations where using a composite PK would be cumbersome and unwieldy and therefore not an optimal choice. Your question is: “if composite primary keys are bad practice…
Why do we use composite key in SQL Server?
This helps to minimize the index size, sorting and updates and; b) it helps avoid the messy and expensive FK constraint updates if you have to change the data in or structure of the table. Thus every table typically will have a primary key that has no relationship to the table data.
Which is the best primary key in a database?
This is sort of a controversial point, since many database designers talk nowadays about using an integer ID auto-generated field as the primary key instead of a composite one defined by the combination of two or more fields. This is currently defined as the “best practice” and, personally, I tend to agree with it.
Can a table key be composite of two columns?
So for choosing whether to have a composite of two columns or a random (probably serial) generated number as the table key, you can have two different keys at once. If data values include a suitable unique term that can represent the row, I’d rather declare that as “primary key”, even if composite, than use a “synthetic” key.