What Does Composite Key Mean?
A composite key, in the context of relational databases, is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined; when taken individually the columns do not guarantee uniqueness.
Techopedia Explains Composite Key
Any column(s) that can guarantee uniqueness is called a candidate key; however a composite key is a special type of candidate key that is only formed by a combination of two or more columns. Sometimes the candidate key is just a single column, and sometimes it is formed by joining multiple columns.
