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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
Question 1 Create a table student with attributes student name, roll number, total marks and percentage. Do the following operations Insert details in to the table Update
Event Occurrence of a process is called event. In other words, the object can receive many input instructions. The changes which occur due to these instructions are known as e
Example :; transfers transfer_amount from x's account to y's account ; Supposes x&y both accounts exist TRANSACTION (x, y, transfer_amount) Start transaction IF X AND Y
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how many hourse have been spent on a certain project
What is a database graph? The partial ordering implies that the set D may now be viewed as a directed acyclic graph, known as a database graph.
Failure Controlling Methods: Failures can be handled using different recovery methods that are talk about later in the unit. But the first question is doing we really require recov
" Wound-wait" scheme : It is based on a preemptive method. It is based on a simple rule: If Ti requests a database resource that is held by Tj
What is relational model feature? A relational model feature is much more data independence than some other database models.
Representing complex relationship among data A database may contain varieties of data interrelated to each other in numerous ways. A DBMS must have the capability to represent
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