A primary key is an identifier that uniquely identifies a row in the table containing data. Keys can also be referred to as primary keys and unique keys. A table’s primary key uniquely identifies each row in that table. Primary keys must not be nullable and can only contain blanks, numbers, or a combination of both.
Question : What is primary key. Choose from the options given below -
Option 1: A Primary key is a field or a combination of fields that can uniquely identify a row/tuple in a table/relation.
Option 2: A Primary key in table/relation is any non-primary key field which also stores unique values for each row just like a primary-key does. But only one key is designated as primary key. So unique refers to a unique non-key field of a table.
Option 3: A Primary key is a field of a table which is the primary key of another table through a foreign key a relationship is established between two tables.
Option 4: None of the above
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