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 algebra’s join (together with WHERE component that specifies equal fields). SQL’s WHERE component isolates rows (i.e., relational algebra’s select). It also helps accomplish relational algebra’s 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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This note was uploaded on 12/17/2011 for the course ACCOUNTING 425 taught by Professor Stebbins during the Fall '11 term at Franklin.

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

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