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Understanding SQL

Access SQL is the language that underlies Access queries, so you need to understand a little bit about it, where it came from, and how it works. Access SQL enables you to construct queries without using the Access Query By Example (QBE) grid. This is necessary, for example, if you must build a SQL statement on the fly in response to user interaction with your application. Furthermore, certain operations supported by Access SQL aren't supported by the graphical QBE grid. You must build these SQL statements in the Query Builder's SQL view. In addition, there are many times when you will want to build the record source for a form or report on the fly. In those situations, you must have command of the SQL language. Finally, you will want to use SQL statements in your ADO and Data Access Objects (DAO) code. For all these reasons, learning SQL is a valuable skill.

What Is SQL, and Where Did It Come From?

SQL is a standard from which many different dialects have emerged. It was developed at an IBM research laboratory in the early 1970s and first formally described in a research paper released in 1974 at an Association for Computing Machinery meeting. Jet 4.0, the version of the Jet Engine provided with Access 2000 and above, has two modes: one supports Access SQL and the other supports SQL-92. The SQL-92 extensions are not available from the user interface. They can only be accessed using ADO. They are covered in a later section of this chapter, “Jet 4.0 ANSI-92 Extensions.”


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