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Define the Query optimisation
The query parser commonly generates a standard initial tree to correspond to an SQL query, with no doing any optimization. Such type of a canonical query tree denotes a relational algebra expression that is extremely inefficient if executed directly. A query commonly has many possible execution strategies, and the process of choosing a appropriate one for processing a query is termed as query optimization. The major guidelines that are applied throughout query optimization are:
a. Combine a cascade of selections
b. Combine a cascade of projections
c. Commute selection and projection
d. Commuting selection with join / cartesian product Commuting projection with join or cartesian product
e. Commute projection with set operations
f. Commute selection with set operations
Relations create the database. They must satisfy various properties, like no duplicate tuples, no ordering of tuples, and atomic attributes, etc. Relations that satisfy these basic
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Convert the following ER - diagram (Entity Relationship Diagram) into a relational database (the primary keys are underlined): 2160_Convert the following ER - diagram into a
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NEED ER DIAGRAM WITH MINIMUM ENTITY AND RELATIONSHIP of Hospital Management System
What are the disadvantages of relational approach? Disadvantages of relational approach: • Substantial hardware and system software overhead • May not fit all business models •
The File Based System File based systems are an early attempt to computerise the manual filing system. For example, a manual file can be set up to hold all the correspondence r
Explain the concept of QBE? Query-by-example represents a visual/graphical approach for accessing information in a database by the use of query templates called as skeleton tab
Three way to handle missing field val
What is banker's algorithm? Banker's algorithm is a deadlock avoidance algorithm that is applicable to a resource-allocation system with multiple instances of each resource ty
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