Questions and Answers
Quales es le functiones principal de la Algebra Relationale?
Que significa PROJECT in Algebra Relationale?
Choose columns/attributes
Que significa SELECT in Algebra Relationale?
Choose rows/tuples
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?
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Quales es le tipos de JOIN in Algebra Relationale?
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Que es un Theta-join?
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Como se define un Equi-join?
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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';
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- 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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