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What is theta join explain?
Theta Join - The theta join operation is an extension to the natural-join operation which permits us to merge selection and a Cartesian product within a single operation. Consider relations r(R) and s(S), and let θ be a predicate on attributes in the schema R ∪ S. The theta join operation r θ s is described as follows:
r θ s = σθ (r x s)
Define instance and schema? Instance: Collection of data stored in the data base at a certain moment is Schema: The overall design of the data base is known as the data base
If R1 and R2 are two union compatible relations or functions, then the result of R3 = R1 ∩R2 is the relation that contains all tuples that are in both the relations In other words,
Explain the Check Clause The CHECK clause is employed to at the end of a CREATE TABLE statement specify table constraints. This is known as table-based constraint because it ap
Given the following relations TRAIN (NAME, START, DEST) TICKET (PNRNO., START, DEST, FARE) PASSENGER (NAME, ADDRESS, PNRNO.) Write SQL expressions for the following queries: No
What are the disadvantages of relational approach? Disadvantages of relational approach: • Substantial hardware and system software overhead • May not fit all business models •
It can be easily defined as: The database must not have any unmatched foreign key values. The term "unmatched foreign key value" means a foreign key value for which there doe
A database named yourusernameFMA has been set up for you to use for this assignment. For the FMA you must create the required tables and run the queries using this database. If y
Why did SAP introduce the extended star schema? Explain why it is reported to be better than the traditional schema model?
Explain Candidate Key and Super Key A super key is a set of one or more than attributes that, taken collectively, permits us to identify uniquely a tuple in the relation. Wher
what is union compatable?
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