Question

What datatypes can't be a PRIMARY KEY, FOREIGN KEY or have a UNIQUE constraint?

a) Integer and Float
b) Character and Text
c) BLOB and CLOB
d) Boolean and Date

Answer 1

BLOB and CLOB data types cannot be used as PRIMARY KEY, FOREIGN KEY, or have a UNIQUE constraint because of their large size and variable content.

Step-by-step explanation:

The data types that cannot be used as a PRIMARY KEY, FOREIGN KEY, or have a UNIQUE constraint in most database systems are BLOB (Binary Large Object) and CLOB (Character Large Object). These types of data are typically used to store large binary or text data such as images, documents, and very long strings which are not suitable for indexing and key constraints due to their size and lack of fixed format.

Data types that can't be a primary key, foreign key, or have a unique constraint are:

BLOB and CLOB: These are data types used to store large binary and character data, respectively. They are not suitable for being used as keys or having unique constraints because they don't have a comparison or equality operation defined on them.

Boolean: Boolean data types represent true/false values. They are not suitable for being used as keys or having unique constraints because they have only two possible values and can result in limited uniqueness.

Date: Date data types represent dates without any time component. Although dates can be used as part of a primary key or foreign key, they are not suitable to be the sole key or have unique constraints because they can have duplicate values within a date range.