lecture-03-intro-sql-relational-algebra

lecture-03-intro-sql-relational-algebra - Introduction to...

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Unformatted text preview: Introduction to RA and SQL Queries and Operations SQL and Relational Algebra T. M. Murali August 30, 2010 T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations What is SQL? I SQL = Structured Query Language (pronounced“sequel”). I Language for defining as well as querying data in an RDBMS. I Primary mechanism for querying and modifying the data in an RDBMS. I SQL is declarative: I Say what you want to accomplish, without specifying how. I One of the main reasons for the commercial success of RDMBSs. I SQL has many standards and implementations: I ANSI SQL I SQL-92/SQL2 (null operations, outerjoins) I SQL-99/SQL3 (recursion, triggers, objects) I Vendor-specific variations. T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations What is Relational Algebra? I Relational algebra is a notation for specifying queries about the contents of relations. I Relational algebra eases the task of reasoning about queries. I Operations in relational algebra have counterparts in SQL. I To process a query, a DBMS translates SQL into a notation similar to relational algebra. T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations What is an Algebra? I An algebra is a set of operators and operands. T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations What is an Algebra? I An algebra is a set of operators and operands. I Arithmetic: operands are variables and constants, operators are + ,- , × , ÷ ,/ , etc. I Set algebra: operands are sets and operators are ∪ , ∩ ,- . T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations What is an Algebra? I An algebra is a set of operators and operands. I Arithmetic: operands are variables and constants, operators are + ,- , × , ÷ ,/ , etc. I Set algebra: operands are sets and operators are ∪ , ∩ ,- . I An algebra allows us to construct expressions by combining operands and expression using operators and has rules for reasoning about expressions. I a 2 + 2 × a × b + b 2 , ( a + b ) 2 . I R- ( R- S ) , R ∩ S . T. M. Murali August 30, 2010 CS4604: SQL and Relational Algebra Introduction to RA and SQL Queries and Operations Basics of Relational Algebra I Operands are relations, thought of as sets of tuples. I Think of operands as variables, whose tuples are unknown. I Results of operations are also sets of tuples. (Later, we will define a relational algebra on bags.) I Think of expressions in relational algebra as queries , which construct new relations from given relations....
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This note was uploaded on 12/24/2011 for the course CS 4604 taught by Professor Cmmalik during the Fall '08 term at Virginia Tech.

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lecture-03-intro-sql-relational-algebra - Introduction to...

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