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Explain the EXISTS and UNIQUE functions of SQL. Give an example for each?
EXISTS: The EXISTS function takes one parameter that is a SQL statement. If any records exist which match the criteria it returns true, or else it returns false. This provides you a clean, well-organized way to write a stored procedure in which does either an insert or update.
UNIQUE: If UNIQUE is particular then only unique values are used to compute the mean.
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Consider the relation PERSON. If you want to display details of persons having age less than or equal to 30 than the select operation will be used as follows: σ AGE The resu
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What is an Index? An index is a small table having only two columns. The first column has a copy of the primary or candidate key of a table and the second column having a set o
Dependency Preservation It is obvious that the decomposition must be lossless so that we do not lose any information from the relation that is decomposed. Dependency preservati
Draw an entity relationship diagram (ERD) for the following situation: A company has a number of employees. Each employee is identified by an Employee_Id. The company wants to st
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Describe the nested-loop join and block-nested loop join. Ans: The block nested- loop join algorithm is as described below: for every block B r of relation R do beg
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