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Relational algebra is made up of which of the following five fundamental operations?
Relational algebra is made up of which of the following five fundamental operations?
Which of the following should you use to ensure that union-compatibility exists between two relations from which you want to create a third relation that does not contain duplicate information?
Which of the following should you use to ensure that union-compatibility exists between two relations from which you want to create a third relation that does not contain duplicate information?
Which of the following SQL statements should you use to restrict a Cartesian product relational algebraic operation to avoid the redundancy of creating a relation that contains every possible row combination from two relations?
Which of the following SQL statements should you use to restrict a Cartesian product relational algebraic operation to avoid the redundancy of creating a relation that contains every possible row combination from two relations?
What is the term for a binary operation that combines two relations where the combination of rows satisfies a predicate?
What is the term for a binary operation that combines two relations where the combination of rows satisfies a predicate?
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Consider the following relational algebraic expression: σ location = 'BldgA' (Employee). Which SQL expression is equivalent to this relational algebraic expression?
Consider the following relational algebraic expression: σ location = 'BldgA' (Employee). Which SQL expression is equivalent to this relational algebraic expression?
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To which of the following is a join operation equivalent?
To which of the following is a join operation equivalent?
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What do the relations known as that require the two relations involved to have the same number of attributes with matching domains?
What do the relations known as that require the two relations involved to have the same number of attributes with matching domains?
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What function does the intersection relational algebraic operation perform?
What function does the intersection relational algebraic operation perform?
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Consider the following SQL statement: SELECT Proj_Mgr., Contractor. FROM Proj_Mgr, Contractor WHERE Proj_Mgr.e_id = Contractor.e_id. What type of operation is represented by the SQL statement?
Consider the following SQL statement: SELECT Proj_Mgr., Contractor. FROM Proj_Mgr, Contractor WHERE Proj_Mgr.e_id = Contractor.e_id. What type of operation is represented by the SQL statement?
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Selection is a unary operation that:
Selection is a unary operation that:
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What function does the union relational algebraic operation perform?
What function does the union relational algebraic operation perform?
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Projection is a unary operation that:
Projection is a unary operation that:
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Which relational algebraic operation creates a new relation containing every possible pair of rows from the two original relations?
Which relational algebraic operation creates a new relation containing every possible pair of rows from the two original relations?
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Consider the following relational algebraic expression: Employee ∪ Proj_Mgr. Which SQL statement is equivalent?
Consider the following relational algebraic expression: Employee ∪ Proj_Mgr. Which SQL statement is equivalent?
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You have two relations from which you can extract data: Employee and Proj_Mgr. Which relational algebraic operation should you use to determine which employees are not project managers?
You have two relations from which you can extract data: Employee and Proj_Mgr. Which relational algebraic operation should you use to determine which employees are not project managers?
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You have two relations from which you can extract data: Proj_Mgr and Contractor. Which relational algebraic operation should you use to determine the project managers who are contractors?
You have two relations from which you can extract data: Proj_Mgr and Contractor. Which relational algebraic operation should you use to determine the project managers who are contractors?
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Which relational algebraic operation is represented by the symbol π?
Which relational algebraic operation is represented by the symbol π?
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Consider the following SQL statement: SELECT Customer.c_id, last_name, first_name, address, city, state, zip, Tour.c_id, tour_no FROM Customer, Tour WHERE Customer.c_id = Tour.c_id. What type of operation is represented by this SQL statement?
Consider the following SQL statement: SELECT Customer.c_id, last_name, first_name, address, city, state, zip, Tour.c_id, tour_no FROM Customer, Tour WHERE Customer.c_id = Tour.c_id. What type of operation is represented by this SQL statement?
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Consider the SQL statement: SELECT * FROM Employee WHERE hire_date = '06-01-2004'; Which relational algebraic expression is equivalent?
Consider the SQL statement: SELECT * FROM Employee WHERE hire_date = '06-01-2004'; Which relational algebraic expression is equivalent?
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What distinguishes an equi-join from a theta-join?
What distinguishes an equi-join from a theta-join?
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Consider the following relational algebraic expression: Employee X Project. Which SQL statement is equivalent to this relational algebraic expression?
Consider the following relational algebraic expression: Employee X Project. Which SQL statement is equivalent to this relational algebraic expression?
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Which symbol indicates a Cartesian product relational algebraic operation?
Which symbol indicates a Cartesian product relational algebraic operation?
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Study Notes
Fundamental Operations of Relational Algebra
- Relational algebra consists of five primary operations: selection, projection, Cartesian product, union, and difference.
Ensuring Union-Compatibility
- To create a third relation without duplicates from two relations, utilize the projection operation.
Restricting Cartesian Products in SQL
- The WHERE clause is essential to limit Cartesian products and reduce redundancy by restricting row combinations.
Theta-Join Definition
- A theta-join is a binary operation that combines two relations based on a predicate satisfied by the rows.
Equivalent SQL Expressions for Selection
- The expression σ location = 'BldgA' (Employee) corresponds to SQL: SELECT * FROM Employee WHERE location = 'BldgA';.
Equivalence of Join Operations
- A join operation is equivalent to a restricted Cartesian product, combining rows based on specific conditions.
Union-Compatible Relations
- Relations that must have the same number of attributes with matching domains are known as union-compatible relations.
Function of Intersection Operation
- The intersection operation yields a new relation containing rows common to both input relations.
SQL Representation of Intersection
- The SQL statement SELECT Proj_Mgr., Contractor. FROM Proj_Mgr, Contractor WHERE Proj_Mgr.e_id = Contractor.e_id represents an intersection of two relations.
Selection Operation Characteristics
- Selection is a unary operation that selects rows from a single relation based on a specified condition.
Function of Union Operation
- The union operation merges rows from two relations into one, ensuring the elimination of duplicate rows.
Characteristics of Projection Operation
- Projection is a unary operation that chooses specific columns from a single relation to produce a new relation.
Cartesian Product Definition
- The Cartesian product is a binary operation generating a new relation with every possible pair of rows from two relations.
Equivalent SQL for Union
- The expression Employee ∪ Proj_Mgr corresponds to SQL: SELECT * FROM Employee UNION SELECT * FROM Proj_Mgr;.
Identifying Non-Project Managers
- To find employees who are not project managers, employ the difference operation.
Finding Common Project Managers
- The intersection operation is used to identify project managers who are also contractors.
Projection Symbol
- In relational algebra, projection is denoted using the symbol π.
SQL Representation of Equi-Join
- The SQL statement SELECT Customer.c_id, last_name, first_name, address, city, state, zip, Tour.c_id, tour_no FROM Customer, Tour WHERE Customer.c_id = Tour.c_id represents an equi-join operation.
Equivalent Expression for Specific SQL Queries
- The SQL statement SELECT * FROM Employee WHERE hire_date = '06-01-2004' is equivalent to the relational algebra expression σ hire_date = '06-01-2004'(Employee).
Distinction Between Equi-Join and Theta-Join
- An equi-join uses only the equality operator in its predicate, while a theta-join can utilize any comparison operator.
SQL Equivalent for Cartesian Products
- The expression Employee X Project corresponds to SQL: SELECT Employee., Project. FROM Employee, Project.
Symbol for Cartesian Product
- In relational algebra, the symbol X signifies the operation of Cartesian product.
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