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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
What subschema expresses ? A subschema expresses the external view. (External schemas are called also called as subschemas)
Consider the subsequent relations along with keys underlined Street (name, location, city) House (number, street_name) Lives (name, house_number) Define the above relations
What is multiple relationship ?
Define single valued and multivalued attributes. Single valued attributes: attributes with a single value for a particular entity are known as single valued attributes. Mult
write-set(T): Each data items that are written by a transaction T
Consider the subsequent relations for a database which keeps track of business trips of salespersons in a sales office: SALESPERSON (SSN, Name, start_year, Dept_no) TRIP (SSN, Fr
Question : Object-Oriented Database (OODM) is defined as a logical data model that captures the semantics of objects supported in object-oriented programming. An Object-Oriente
Use a Set operator to create a list of academics who have written or co-written less than 5 papers and also have greater than 3 interests. List their academic number in the output.
What are uncommitted modifications? The immediate-modification technique permits database modifications to be output to the database whereas the transaction is still in the act
The Locking Protocol: To manage concurrency related problems we use locking. A lock is mainly a variable that is associated with a data item in the database. A lock can be located
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