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Questions and Answers
What is the main property of relational algebra operations?
What is represented by the Greek letter Sigma (σ)?
What is the result of the set difference operation r - s?
What is the purpose of the rename operator?
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What is the Cartesian Product operation?
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What is the condition for applying the division operator?
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What is the result of the division operator?
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What is the symbol used to represent the join operation?
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What type of join includes only those tuples that satisfy the matching criteria?
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What type of join uses all kinds of comparison operators?
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Study Notes
Relational Algebra
- Relational algebra operations work on one or more relations to define another relation without changing the original relations.
- Both operands and results are relations, so output from one operation can become input to another operation.
- Allows expressions to be nested, just as in arithmetic, which is called closure property.
Basic Operations on Relations
- Selection: selects tuples that satisfy the given condition.
- Projection: returns its argument relation with specific attributes left out and removes duplicate rows.
- Union: combines two or more relations.
- Difference: returns the set of elements contained in one relation but not in another.
- Cartesian Product: associates every tuple of one relation with every tuple of another relation.
- Joins: combines two or more relations based on some conditions.
Select Operation
- Represented with the lower case letter Sigma (σ).
- Selects tuples that satisfy the given condition.
- The input relation to the select operation is only one.
Project Operation
- Represented with the letter π.
- Returns its argument relation with specific attributes left out.
- Removes duplicate rows.
Union Operation
- Combines two or more relations.
- Relations must be union compatible (or type compatible).
Set Difference Operation
- Returns the set of elements contained in one relation but not in another.
- Relations must be union compatible (or type compatible).
Set Intersection Operation
- Returns the set of elements common to both relations.
- Relations must be union compatible (or type compatible).
Cartesian Product Operation
- Associates every tuple of one relation with every tuple of another relation.
- Denoted by a cross symbol.
- Notation: r x s (all possible pairing).
Rename Operator
- It is a unary operator (input is a single relation).
- It is used to give the name of our choice to a new relation obtained after using any linear algebra operation.
- Notation: ρ (R,E).
Division Operator
- Used to find the tuples that are associated with every tuple of another relation.
- Notation: A/B or A ÷ B.
- Can be applied if and only if the attributes of B are a subset of A.
Join Operation
- Combines two or more relations based on some conditions.
- It is a combination of Cartesian product and selection process.
- Join types: Inner Join, Outer Join (Left, Right, Full), Theta Join, Equijoin, Natural Join.
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Description
Learn about relational algebra operations that work on one or more relations to define another relation, and how they can be nested like arithmetic expressions.
