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Questions and Answers
Quales es le functiones principal de la Algebra Relationale?
Quales es le functiones principal de la Algebra Relationale?
Que significa PROJECT in Algebra Relationale?
Que significa PROJECT in Algebra Relationale?
Choose columns/attributes
Que significa SELECT in Algebra Relationale?
Que significa SELECT in Algebra Relationale?
Choose rows/tuples
Qual es le resultatato de SELECT project_manager FROM project WHERE project_code = '25-5A'?
Qual es le resultatato de SELECT project_manager FROM project WHERE project_code = '25-5A'?
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Qual es le definition de CARTESIAN PRODUCT?
Qual es le definition de CARTESIAN PRODUCT?
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Quales es le tipos de JOIN in Algebra Relationale?
Quales es le tipos de JOIN in Algebra Relationale?
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Que es un Theta-join?
Que es un Theta-join?
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Como se define un Equi-join?
Como se define un Equi-join?
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Qual es le diferentes pasos de un Natural Join?
Qual es le diferentes pasos de un Natural Join?
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Study Notes
Algebra Relational
- Procedural paradigm utilized in database querying.
- Cada operator aplica a AT MAXIMUM du relationes simultaneamente.
- Octo functiones principali incluse: SELECT, PROJECT, CARTESIAN PRODUCT, JOIN, INTERSECTION, UNION, DIFFERENCE, DIVISION.
PROJECT - π (pi)
- Utilizado pro seleccionar columnas o atributos de un relation.
SELECT - σ (sigma)
- Utilizado pro seleccionar filas o tuplas de un relation.
Multiple Actions - PROJECT (SELECT)
- Exemplo de SELECT:
SELECT project_manager FROM project WHERE project_code = '25-5A';
- Equivalente in Algebra Relational: π_project_manager (σ_project_code = '25-5A' PROJECT).
CARTESIAN PRODUCT - X
- Combine omne filas de un relation con omne filas de un altere relation.
- Representato como no_row_1 x no_row_2.
JOIN (4 tipos)
- Include quatro variantes de joins:
- Theta-join
- Equi-join
- Natural join
- Outer join
Theta-join - ⨝_θ
- An operator que unifica tabulas usando un comparison operator d'inequality (ex. <, >, =).
Equi-join (2 passos)
- Join basato super equality entre valores in columnas communs.
- Processus:
- Passo 1: R1 X R2
- Passo 2: Deleter filas non correspondentes.
Natural Join - ⨝ (3 passos)
- Similar al equi-join, pero elimina un de columnas duplicate in le resultato.
- Processus:
- Passo 1: R1 X R2
- Passo 2: Deleter filas non correspondentes.
- Passo 3: Deleter le columna duplicate.
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