Question

A primary key must contain a value and the value must be

Answer 1

Answer:

A primary key must contain unique values. If the primary key consists of multiple columns, the combination of values in these columns must be unique. A primary key column cannot contain NULL values. It means that you have to declare the primary key column with the NOT NULL attribute.

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Explanation:

Answer 2

Answer:

A primary key must contain a value and the value must be unique

Explanation:

• The main key in a database serves to give a map of the data. A primary key is a unique identifier for all table records in a relational database table column (or set of columns). The following are the fundamental characteristics of a primary key: Each row of data must have a unique value. It cannot have any null values.
• A primary key's principal function is to implement a relationship between two tables in a relational database; it's not called that for nothing! In particular, the main key is the "target" to which a foreign key might refer.
• A primary key is a unique relational database table field (or set of columns) that is used to identify each table entry. To easily interpret data within the database, a primary key is employed as a unique identifier. A table can only have one main key. The following are the fundamental characteristics of a primary key:
• Each row of data must have a unique value.
• It cannot have any null values.
• A primary key value must be assigned to each row.
• A primary key can employ one or more fields that are already existing in the underlying data model, or it can be built from scratch.

Reference Link

• https://brainly.in/question/48275854
• https://brainly.in/question/8227267