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How does a query tree represent a relational algebra expression? Discuss any three rules for query optimisation, giving example as to when should each rule be applied.
Ans: A query tree is a tree structure which refers to a relational algebra expression. It denotes the input relations as leaf nodes of the tree, and denotes the relational algebra operations as internal nodes. An execution of the query tree contains executing an internal node operation while its operands are available and after that replacing that internal node by the relation which results from executing the operation. The execution terminates while the root node is executed and generates the result relation for the query. For instance, the query tree for the relational algebra expression
∏E_No =(σp_No = 'DB2003' (Assigned_To) :
The three rules for query optimization are like this:
∏1(∏2(......∏n ( R))) ≡ ∏1(R )
∏A1, A2,......An (σC (R ) ≡ σC (∏A1, A2, ......An (R ))..... ))
σC1 AND C2 AND ....AND Cn (R ) ≡ σC1 (σC2(....(σCn (R ))....))
Gyan Gurukul is a software company that provides software related solution. Ashutosh Dubey who is the director of Gyan Gurukul want a three-level schema architecture for the Gyan G
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List the steps for converting state diagram to the code. a) Finding major control path b) Finding the conditional statements c) Finding the loops d) Finding error ro
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Why did SAP introduce the extended star schema? Explain why it is reported to be better than the traditional schema model?
One-to-many : An entity in A is related with any number of entities in B. An entity in B is related with at the most one entity in A. Example: Relationship between faculty and d
notes about update opreation
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