5 Reading (Free web hosting with ftp) and Writing Data with SQL Any
5 Reading and Writing Data with SQL Any sufficiently advanced technology is indistinguishable from magic. (Arthur C. Clarke) SQL helps to explain relational database modeling. None of this is magic, and is much easier to understand than you might think. This chapter shows how the relational database model is used from an application perspective. There is little point in understanding something, such as relational database modeling, without seeing it applied in some way, no matter how simple. With that in mind, this chapter looks at how a database model is accessed when it contains data in a database. A relational database model contains tables, and the records in those tables are accessed using Structured Query Language (SQL). SQL is used to create the database access sections of applications. When a database model is correctly designed, creation of SQL code is a simple process. Great difficulties in coding of SQL queries in particular can often indicate serious database model design flaws. This book is all about relational database modeling; therefore, it is necessary to explain only the basis of SQL in this book as pertaining directly to helping in the understanding of relational database modeling. How can describing the basic details of SQL help with the understanding of relational database modeling? The answer to this question is very simple. SQL uses a relational database model to change data in a database, and to retrieve data from that database. SQL essentially applies all the structures created by the relational database modeling process. SQL and particularly SQL queries and their simplicity is a direct result of the underlying structure of a database model. In other words, the better and more appropriate a database model is, the easier building SQL code for applications will be. Another way to look at this is that a database model is most easily utilized by applications, when matching application structure. It makes perfect sense to describe the basics of using SQL because it demonstrates the use of a relational database model in action.
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