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Questions and Answers
What does the symbol σ represent in relational algebra?
What does the symbol σ represent in relational algebra?
What is the function of the π symbol in relational algebra?
What is the function of the π symbol in relational algebra?
It represents the PROJECT operation, selecting columns from tables and eliminating duplicates.
The ρ symbol in relational algebra represents a unary relational operation called RENAME.
The ρ symbol in relational algebra represents a unary relational operation called RENAME.
True
What does the U symbol denote in relational algebra?
What does the U symbol denote in relational algebra?
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What does the ∩ symbol signify in relational algebra?
What does the ∩ symbol signify in relational algebra?
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The - symbol in relational algebra is known as DIFFERENCE/MINUS/EXCEPT.
The - symbol in relational algebra is known as DIFFERENCE/MINUS/EXCEPT.
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Does the X symbol in relational algebra require type compatibility?
Does the X symbol in relational algebra require type compatibility?
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For two relations to be _____ compatible, they must have the same number of attributes and their domains must be type compatible.
For two relations to be _____ compatible, they must have the same number of attributes and their domains must be type compatible.
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Study Notes
Relational Algebra Symbols
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σ (SELECT)
- Represents a unary relational operation applied to a single relation.
- Can involve boolean conditions.
- Example: σ(Dno=4 AND Salary>2500)(EMPLOYEE) selects tuples from EMPLOYEE with department number 4 and salary exceeding 2500.
- This operation is commutative.
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π (PROJECT)
- A unary relational operation that selects specific columns from a relation while discarding others.
- Eliminates duplicate entries in the result.
- Example: π(FName, LName, Salary)(EMPLOYEE) retrieves each employee's first name, last name, and salary.
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ρ (RENAME)
- Denotes a unary relational operation for renaming attributes in a relation.
- Does not involve additional data manipulation.
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U (UNION)
- Combines all tuples from two relations (R and S), including duplicates.
- Results in a single relation containing tuples from either relation.
- Both relations must be type compatible.
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∩ (INTERSECTION)
- Includes all tuples common to both relations R and S.
- The result maintains the attribute names from relation R.
- Requires type compatibility between the involved relations.
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- (DIFFERENCE/MINUS/EXCEPT)
- Denotes the set of tuples in relation R that are not found in relation S.
- Both relations must be of the same type to perform this operation.
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X (CARTESIAN PRODUCT)
- Combines every tuple of one relation with every tuple of another.
- Type compatibility is not a requirement.
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Type Compatible
- Two relations are type compatible if they possess the same number of attributes.
- The domains of corresponding attributes must also be compatible (i.e., dom(Ai) = dom(Bi) for corresponding attributes).
- Critical for operations such as union, intersection, and difference.
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Description
Test your knowledge of relational algebra with these flashcards focusing on key symbols and their definitions. Learn about operations such as SELECT and PROJECT, as well as how they apply to relational databases. Perfect for students and professionals looking to strengthen their understanding of database concepts.
