Question

Explain about primary key super key candidate key alternate key composite key foreign key?

Answer 1

A primary key is a special relational database table column (or combination of columns) designated to uniquely identify all table records. A primary key'smain features are: It must contain a unique value for each row of data. It cannot contain null values. A superkey is a combination of columns that uniquely identifies any row within a relational database management system (RDBMS) table. A candidate key is a closely related concept where the superkey is reduced to the minimum number of columns required to uniquely identify each row.A candidate key is a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is unique, and it is called the primary key.Alternate keys may be used like a primary key in a single-table select. A unique key that has migrated to another entity. At the most basic definition, "a key is a unique identifier", so unique key is a pleonasm. Keys that are within their originating entity are unique within that entity.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.A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.

Answer 2

Explanations of keys are given below:-

Explanation:

Primary key:-

• The primary key is a segment or group of columns in a table that uniquely defines each row in that table.
• The Primary Key can not be a repeat, meaning that the same value can not appear more than once in the table. The table could not have more than one primary key.

Super key:-

• A superkey is a single or multiple key categories that distinguish rows in a table.
• The super key can have external features that are not required for specific identification.

Candidate key:-

• The candidate key is a collection of features that uniquely identify iterators in a list.
• Candidate Key is a special button with no-repeat features.

Alternate key:-

• The keys that are not the main key are considered the Alternative Key.
• The Alternate Key is a row or set of sections in a list that specifically defines every row in that table.

Composite key:-

• A composite key is a combination of two or more columns that uniquely distinguish rows in a table.
• The combination of columns ensures individuality, but no individual individuality is assured.

Foreign key:-

• The Foreign Key is a column that defines a connection between two tables.
• It serves as a boundary-reference among two tables, since it corresponds to the primary key of a table.

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