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Ans. The clustered index determines how the data is stored in the rows of a table.The non-clustered index stores the data at a single place and the indexes are stored at another place.
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Ans. Usually Relational Databases are optimized for writing. Some exception being usage of indices where indices needs to be updated after insertion and eventually helps with Log(n) reading time.
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Q38. What is read and write optimization in relation to databases ? Which database facilitates read optimization and which facilitates write optimization ?
Ans. We can have 2 entities i.e EMPLOYEE and ADDRESS and can have a relationship Table , EMPLOYEE_ADDRESS having one to may relationship between the two.
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Ans. Normalization is the process of splitting one Table into multiple so as to avoid Data duplication whereas Denormalization is the process of reducing Tables that creates data duplication but would remove joins in the queries.
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Ans. ORM is the mapping technique, which maps object with relational data model. As we know that in java we need objects we can not user data in relational(in table form). So ORM is set of guideline which allows us to map relational data model in object form.
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Ans. Ternary operator , also called conditional operator is used to decide which value to assign to a variable based on a Boolean value evaluation. It is used as
condition ? value1 : value2
For example
int y = (x > 0) ? x:0; // assign x if it's greater than 0, else assign 0
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Ans. There is no specific order in which database fires the triggers if they are for the same operation. If we need to have a specific order for their execution, we should have them all in a stored procedure and the procedure should get executed upon the event.
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Ans. It's the way for synchronization wherein we can store version information in the table , so that if the same entity is updated by two transactions, the last to commit changes is informed of the conflict, and does not override the other transaction's work.
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Ans. Primary Key constraint means that the column(s) should be unique and doesn't allow null. So Primary key constraint implies unique and not null constraint too.
Unique constraint implies not null constraint too as allowing null would violate uniqueness on those columns.
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