CLOUD COMPUTING
DATABASE MANAGEMENT
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
Candidate key field
|
|
|
Foreign key
|
|
|
Primary key field
|
|
|
Alternate key field
|
Detailed explanation-1: -PRIMARY KEY in DBMS is a column or group of columns in a table that uniquely identify every row in that table. The Primary Key can’t be a duplicate meaning the same value can’t appear more than once in the table.
Detailed explanation-2: -In the Orders table it is called a foreign key. A foreign key, simply stated, is another table’s primary key.
Detailed explanation-3: -A primary key that made up of more than one attribute is known as a composite key. Below shows an example of a composite key. Each instance of the entity Work can be uniquely identified only by a composite key composed of Employee ID and Project ID.
Detailed explanation-4: -Foreign key columns are frequently used in join criteria when the data from related tables is combined in queries by matching the column or columns in the foreign key constraint of one table with the primary or unique key column or columns in the other table.