COMPUTER SCIENCE AND ENGINEERING
SQL
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Statement 1:A relation can have multiple candidate keys
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Statement 2:A relation can have multiple primary keys
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Statement 3:A relation can have multiple columns with Unique constraint
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None of the above
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Detailed explanation-1: -Primary keys must have UNIQUE values and should not have NULL values. A table can only have ONE primary key, and this primary key might be made up of single or many columns (fields).
Detailed explanation-2: -Answer and Explanation: The statement that is false regarding primary key is: Only parent tables must have a primary key.
Detailed explanation-3: -Each table can only have one primary key. Access can automatically create a primary key field for you when you create a table, or you can specify the fields that you want to use as the primary key. This article explains how and why to use primary keys.
Detailed explanation-4: -A relational database must have only one primary key. Every row of data must have a primary key value and none of the rows can be null.