TAILIEUCHUNG - Understanding SQL

SQL: The Complete Reference provides an in-depth discussion of SQL fundamentals, modern SQL products, and SQL's role in trends such as data warehousing, "thin-client" architectures, and Internet-based e-commerce. This book is your one-stop. | Part 9 Articles A Understanding SQL B Exporting Data C Visual Basic Function Reference D Internet Explorer Web Page Color Names A1 A45 A49 A59 A1 Part 9 Articles Article A Understanding SQL SQL Select Queries .A4 SQL Action Underlying every query in Microsoft Access is the SQL database command language. Although you can design most queries using the simple Access design grid or the view function or stored procedure designer in an Access project file Access stores every query you design as an SQL command. When you use one of the designers Access creates the SQL for you. However for advanced types of queries that use the results of a second query as a comparison condition you need to know SQL in order to define the second query called a subquery . Also you cannot use the design grid to construct all the types of queries Access is capable of handling you must use SQL for some of them. As you learned in Chapter 18 Building Queries in an Access Project understanding SQL is essential to building queries in SQL Server. y m n Note This article does not document all the syntax variants accepted by Access but it does cover all the features of the SELECT statement and of action queries. Wherever possible ANSI-standard syntax is shown to provide portability across other databases that also support some form of SQL. You might notice that Access modifies the ANSI-standard syntax to a syntax that it prefers after you define and save a query. You can find some of the examples shown in the following pages in the sample database. When an example is in the sample database you ll find the name of the sample query in italics immediately preceding the query in the text. For a discussion of the syntax conventions used in this article see the Conventions and Features Used In This Book section in the book s front matter. k How to Use This Article This article .

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