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SQL Set Operators

SQL Set Operators   Traditional Set Operators: Union Compatibility:     Requirement for the traditional set operators.    Strong requirement.                         - Same number of columns.                         - Each corresponding column is compatible.                         - Positional correspondence.     Apply to similar tables by removing columns first. SQL UNION Example:           Example 1: Retrieve basic data about all university people.                     SELECT FacNo AS PerNo, FacFirstName                                      ...
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Entity Relationship Model

Entity Relationship Model

    Data modeling:

             A technique for organizing and documenting a system’s data. Sometimes called database modeling. 

    Entity relationship diagram (ERD):

            A data model utilizing several notations to depict data in terms of the entities and relationships described by that data.

    Purpose of E-R Model:

  • Facilitates database design.
  • Express logical properties of mini-world of interest within enterprise - Universe of Discourse.
  • Conceptual level model.
  • Not limited to any particular DBMS.
  • E-R diagrams used as design tools.
  • A semantic model – captures meanings.

    Symbols used in E-R Diagram:

  • Entity – rectangle  
  • Attribute – oval
  • Relationship – diamond
  • Link - line


      


ER diagram:






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SQL Set Operators

SQL Set Operators   Traditional Set Operators: Union Compatibility:     Requirement for the traditional set operators.    Strong requirement.                         - Same number of columns.                         - Each corresponding column is compatible.                         - Positional correspondence.     Apply to similar tables by removing columns first. SQL UNION Example:           Example 1: Retrieve basic data about all university people.                     SELECT FacNo AS PerNo, FacFirstName                                      ...
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  d. Insert a new row in the Location table related to the Facility row in modification problem (c). The new row should have “Door” for the location name. Query Formulation + Result Snapshot Our Official Website :  Web Conquerors  (https://www.webconquerors.com/)  Want to get digital services?  Contact US Want to know about our services?  Our Services
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Correction For ERD

 d. For each consistency error in Figure 1, you should identify the consistency rule violated and suggest possible resolutions of the error. The ERD has generic names to help will concentrate on finding diagram errors rather than focusing on the meaning of the diagram. Answer:                Entity6 is violation of the Primary key rule. As there are 3 attributes from within Entity6 that are marked as primary key. Entity6 also violates the Identifying relationship rule, as there is no foreign key in the Entity6 table to identify the item from Entity7. Since this a weak entity type, the cardinality must be 1:1, which it is not. Entity2 is a violation of the Identifying relationship rule due to it not being a weak entity type when there is an identifying relationship. Our Official Website :  Web Conquerors  (https://www.webconquerors.com/)  Want to get digital services?  Contact US Want to know about our services?  ...
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