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What is Nested Queries explain in details?
Nested Queries - A SELECT query could have subquery(s) in it. While a SELECT query having another SELECT query in it, is known as nested query. A few operations cannot be performed along with single SELECT command or along with join operation. There are some operations that can be performed along with the help of nested queries (also referred to as subqueries). For instance, we want to calculate the second highest salary:
SELECT MAX(SAL) FROM EMP WHERE SAL < (SELECT MAX(SAL) FROM EMP)
Some operations can be performed both through Join and subqueries. The Join operation is costlier in terms of space and time. Thus, the solution based on subqueries is preferred.
Explain data independence ? Data independence is the capacity to modify the schema at one stage of a database system without having to change the schema at the further level.
Update or Modify operation alters the existing values. If these operations alter the value that is the foreign key also, the only check need is the similar as that of the Insert op
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Explain the Weak Entity Set An Entity set which does not have sufficient attribute to make a primay key is known as weak entity set. For instance, dependents of an employee in
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What are the Objectives of Advance object design After this unit, you shall be able to: combine three OOAD models to obtain operations on the classes; develop algo
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Hi is anyone well versed in accounting information systems available now to help me work through an important assignment due tomorrow at noon?
What are the aggregate objects in the data dictionary? Views Match codes Lock objects.
Explain differance between Primary and secondary storage ? Primary and secondary storage Computer storage is classified within primary(main) memory and secondary(per
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