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(a) Design a query plan for the following distributed query: An application at site B wants to compute a join of STUDENT ?Id=StudId TRANSCRIPT where STUDENT (Id,Major) is at site B and TRANSCRIPT (StudId, CrsCode) is at site C. The result should be returned to B. Assume that semijoin is not used. Also assume that
(b) Estimate the cost of computing σMajor='CS' (STUDENT) ?Id = StudId TRANSCRIPT using the semijoin strategy. Use the sizes of the STUDENT and TRANSCRIPT relations and of their attributes from the part (a) above. In addition, assume that 10% of the students major in CS. Compare this with the solutions in part (a) above that do not use the semijoin.
What is the use of with clause in SQL? The with clause gives a way of defining a temporary view whose explanation is available only to the query in which the with clause occurs
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Submit SQL SELECT Statements to demonstrate several reports off your database, according to the following guidelines: You must submit at least 5 SELECT Statements. Each
Shared lock or Read Lock It is requested by a transaction that needs to just read the value of data item. A shared lock on a data item does not permit an exclusive lock
Which operator is Cartesian product in relational algebra? Cartesian product in relational algebra is a binary operator. (It requires two operands. e.g., P X Q)
Describe Database state in details? Database state: The actual data within the database at a particular moment in time is known as a database state.
how to find entities
Key to represent relationship amongs tables is called ? A Key that represent the relationship between tables is called Foreign Key.
What are partial, alternate,, artificial, compound and natural key? Partial Key: It is a set of attributes that can uniquely recognize weak entities and that are related to s
What is key ? Key - A single attribute or a combination of two or more attributes of an entity set which is used to recognize one or more instances (rows) of the set (table) is
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