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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
Define hot swapping? Hot swapping permits the removal of faulty disks and changes it by new ones without turning power off. Hot swapping decreases the mean time to repair.
Explain Relational model and their use in DBMS? Relational Model - The relational model was first introduced through E.F. Codd of the IBM Research in the year of 1970. The mode
Durability : This property necessitates that once a transaction has committed, the changes made by it be never lost because of subsequent failure. Thus, a transaction is also a bas
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,
what are the type of the database
In how many parts events are classified Events are classified as four types in UML 1. Signals 2. Calls 3. Passing of Time 4. Change in State
explaination
What is the use of rename operation? Rename operation is used to rename both relations and an attributes. It uses the as clause, taking the form: Old-name as new-name.
Consider student (std_id, std_name, date_of_birth, phone, dept_name). Put the data for a student with student id200, name arun, birth date 1 February, 1985, phone number (01110 328
A database to track your progress in your college program will track your progress towards graduation! A database that has information containing the classes that you have taken, c
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