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Define the five basic operators of relational algebra?
Five basic operators of relational algebra are:1. Union (∪∪∪∪) - Selects tuples which are in either P or Q or in both of them. The duplicate tuples are eliminated.R = P ∪ Q2. Minus (-) - Removes generally common tuples from the first relation.R = P - Q3. Cartesian Product or Cross Product (××××) - The cartesian product of two relations is the concatenation of tuples belonging to the two relations and consisting of all probable combination of the tuples.R = P × Q 4. Projection (ππππ) - The projection of a relation is described as a projection of all its tuples over a few set of attributes, i.e., it yields a vertical subset of the relation. It is used to either decrease the number of attributes (degree) in the resultant relation or to reorder attributes. The projection of a relation T on the attribute A is denoted through πA(T).5. Selection (σσσσ) - Selects only some of the tuples, those satisfy given criteria, from the relation. It yields a horizontal subset of a given relation, i.e., the action is defined over a complete set of attribute names but just a subset of the tuples are involved in the result.R = σB(P)
project on dbms
Explain entity integrity and referential integrity rules within relational model. Show how these are realized in SQL? Entity Integrity Rule - No primary key value could be nu
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.
The File Based System File based systems are an early attempt to computerise the manual filing system. For example, a manual file can be set up to hold all the correspondence r
I want to fragment existing table using java code... help me..!!
What is relationship? Give examples A relationship is an association between several entities. Example: A depositor relationship associates a customer with every account tha
Explain the term- Data Flows Data Flows: A data flow connects output of an object or process to input of another process or object. It represents an in-between data value wit
What is Alternate Key Alternate Key: This is the candidate key which is not taken as the primary key of the table. They are named so because although not the primary key, the
What is DDL? Make a list of commands with short description used in DDL Ans: Data Definition Language that is abbreviated as DDL is a computer language for defining data struct
We define a view in SQL through using the create view command. To describe a view, we must provide the view a name and must state the query in which computers the view. The form of
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