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Describe the Composite Key
Composite Key: Sometimes one key is not enough to uniquely recognize a row. E.g. in a single class Roll is enough to search a student, but in the whole school, merely searching by the Roll is not enough, because there could be 10 classes in the school and every one of them may have a certain roll no 5. To uniquely recognize the student we have to say something like "class VII, roll no 5". So, a combination of two or more attributes is combined to make a unique combination of values, such as Class + Roll.
Consider the relation PERSON. If you want to display details of persons having age less than or equal to 30 than the select operation will be used as follows: σ AGE The resu
Hashed File Organisation Hashing is the most common form of purely random access to a database or file. It is also used to access columns that do not have an index as an optimi
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Explain mechanism of nested queries? SQL gives a mechanism for nesting subqueries. A subquery is a select from where expression that is nested within one more query. A common u
Differentiate strict two phase locking protocol and rigorous two phase locking protocol. In strict two phase locking protocol all exclusive mode locks taken by a transaction is
Describe Hashing in DBMS? Hashing: Hashing is a technique to store data within an array so which storing, searching, inserting and deleting data is fast (in theory it's O(1))
Relational Algebra is a set of basic operations used to influence the data in relational model. These operations allow the user to specify basic retrieval request. The result of re
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What is foreign key? A relation schema r1 derived from an ER schema may contain among its attributes the primary key of another relation schema r2.this attribute is known as a
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