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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
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Example : Create a sequence named SEQSS that starts at 105, has a step of 1 and can take maximum value as 2000. CREATE SEQUENCE SEQSS START WITH 105 INCREMENT BY 1 MAX VA
#question.ERD of any car
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Attribute Preservation This is a easy and obvious necessity that includes preserving all the attributes that were there in the relation that is being decomposed.
Describe the difference between a one-to-many and a many-to-many relationship. Which logical data structures comprise one-to-many and which comprise many-to-many relationship?
Special comparison operator used in where Clause a. between. ...and...It gives range among two values (inclusive) Example: SELECT ENAME, SAL FROM EMP WHERE SAL BETWE
write on the various type of relationalkey
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