Assignment 6-1 - component is used for identifying the...

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D1. Relational Algebra : Three main operators: Select which includes only certain rows from a database table in its “answer”, Project which includes only certain columns from a database table in its “answer”, and Join which combines two or more database tables on the basis of one or more common attributes. This provides the conceptual basis for SQL and QBE. Structured Query Language (SQL): The user enters commands according to a pre-defined syntax to retrieve desired data. Each query statement follows the same structure: SELECT attribute name(s), FROM table name(s), WHERE criteria are met. SQL’s SELECT component isolates columns (i.e., relational algebra’s project). SQL’s FROM
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Unformatted text preview: component is used for identifying the table(s) involved if >1 table, helps accomplish relational algebras join (together with WHERE component that specifies equal fields). SQLs WHERE component isolates rows (i.e., relational algebras select). It also helps accomplish relational algebras join and may be left blank for single-table queries that retrieve all rows D2. Query by Example (QBE): The user starts with a sample of the table(s) columns and marks the fields he or she wants to include in the answer. Defaults are available for summarizing and manipulating the data....
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Assignment 6-1 - component is used for identifying the...

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