3024-Chap13 - 13. USING QUERIES IN ACCESS Now that you know...

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13. USING QUERIES IN ACCESS Now that you know the steps in designing a relational database, creating the database, and populating it, let’s examine how we can use the database content. To extract information, queries are used. When a query is sent to a relational database, the database software (DBMS) finds the answer from the available tables, then delivers the answer to you in the form of a new table. 2010 John P. Shewchuk ISE 3024 Course Notes 13 – 1
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g to find which titles are available as audio books DBMS E.g., to find which titles are available as audio books, DBMS - reads MediaType table, opies all rows having either “Audio” or “Both” for the - copies all rows having either Audio or Both for the format field, - puts these in a new table, and finally - delivers the new table. many instances queries require combining and filtering In many instances, queries require combining and filtering data from multiple tables. Whether a query involves data from one table or many, we must always specify queries carefully to get correct (and seful) answers. 2010 John P. Shewchuk ISE 3024 Course Notes 13 – 2 useful) answers.
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hree main approaches for specifying queries: Three main approaches for specifying queries: • Query Wizard (or other similar utility) uery By Example ( BE) • Query By Example (QBE) • Structured Query Language (SQL) ccess is capable of all three of these However the best Access is capable of all three of these. However, the best choice overall when using Access is QBE. • Query Wizard – extremely limited. • SQL: more difficult. 2010 John P. Shewchuk ISE 3024 Course Notes 13 – 3
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o we will use QBE exclusively in this chapter using our So, we will use QBE exclusively in this chapter, using our Anna’s Books Access 2007 database from the end of the last chapter ( AnnasBooks_12.accdb ). AnnasBooks_13.accdb : Anna’s Books database as it would exist at the end of this chapter. • created and populated as per Chapter 12. • queries as per this chapter. These files can be downloaded from Scholar: Scholar: Resources Application Files 2010 John P. Shewchuk ISE 3024 Course Notes 13 – 4 Chapters 12-14: MS Access
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13.1 Basic Relational Operations Every relational query consists of a sequence of operations. Each operation has one or two input tables. The operation reads the contents of the input table(s) and produces a new ble table. Four basic relational operations: Select operations – Project operations – subset of columns of original table. Join operations – combine columns of input tables. et perations ws come from one or other of input 2010 John P. Shewchuk ISE 3024 Course Notes 13 – 5 Set operations rows come from one or other of input tables.
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13.1.1 Select Operations A select operation selects rows from an input table that atch some criteria match some criteria.
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This note was uploaded on 02/14/2010 for the course ISE 3024 taught by Professor Staff during the Spring '08 term at Virginia Tech.

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3024-Chap13 - 13. USING QUERIES IN ACCESS Now that you know...

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