Which of the following statements is not true when considering primary keys and secondary keys
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Prerequisite – Keys in Relational Model Show For better understanding of primary key we take table named as Student table, having attributes such as Roll_number, Name, Batch, Phone_number, Citizen_ID.  The roll number attribute can never have identical and NULL value, because every student enrolled in a university can have unique Roll_number, therefore two students cannot have same Roll_number and each row in a table is uniquely identified with student’s roll number. So, we can make Roll_number attribute as a primary key in this case. Unique key constraints also identifies an individual tuple uniquely in a relation or table. A table can have more than one unique key unlike primary key. Unique key constraints can accept only one NULL value for column. Unique constraints are also referenced by the foreign key of another table. It can be used when someone wants to enforce unique constraints on a column and a group of columns which is not a primary key. For better understanding of unique key we take Student table with Roll_number, Name, Batch, Phone_number, and Citizen_ID attributes. Roll number attribute is already assigned with the primary key and Citizen_ID can have unique constraints where each entry in a Citizen_ID column should be unique because each citizen of a country must have his or her Unique identification number like Aadhaar Number. But if student is migrated to another country in that case, he or she would not have any Citizen_ID and the entry could have a NULL value as only one NULL is allowed in the unique constraint. Key Differences Between Primary key and Unique key: Primary key will not accept NULL values whereas Unique key can accept NULL values.
Comparison Chart:
Options CORRECT ANSWER : Primary key may contain duplicate values
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Which of the following statements is not true about a primary key?Primary key can be composite - made up of two or more columns. Thus the third option(Primary key can not be applied for multiple columns)(false) correct as well.
Which of the following statements about primary and foreign key is not true?Option d statement is incorrect. Because Primary key name and the foreign key name need not be same, they can have different names. Every table can have a primary key. And the primary key can be single field or a combination of fields.
Which of the following statements about primary keys are true?True statements: 3, 4.
A primary key cannot be NULL. 2. It is mandatory for the primary key to be given a value when a new record is inserted. 4.
Which of the following are true about a primary key Mcq?Explanation: The primary key is a single or combination of the field that identifies each record in a table uniquely. It cannot take a NULL value. A table can have only one primary key.
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