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| The first questions to ask are what is SQL and how do you use it with databases? SQL has three main roles: Introducing SQL Queries SELECT CarModel The SELECT statement tells the database system that you want to select some data from the database. You then list the data you want, in this case CarModel data, which is a field name. You then specify the place the data needs to be taken from, in this case a table called CarSales. Finally, you have a condition. The statement above specifies that you want only the data where certain conditions are true. In this case, the condition is that the CarSoldDate is between the first and thirty-first of May 2005. Comparing SQL to Other Programming Languages 1. Load the sales data into the computer’s memory.
SQL, however, is a declarative language, which means that instead of telling it what to do to get the
results you want, you simply tell it what you want, and it figures out what to do and comes back with
the results. In the car sales example, if you were using SQL, you’d specify the results you want, something
like this: Understanding SQL Standards Year Name Also Known As Changes 1989 SQL-89 Only small revision of the original standard 1992 SQL-92 SQL2 Major update of the original standard and still the most widely supported standard 1999 SQL-99 SQL3 Update of the 1992 standard adding new ways of selecting data and new rules on data 2003 SQL-2003 Introduced XML support and fields with autogenerated values The SQL you write works on most RDBMSs with only minor modifications. There are times when the various RDBMSs do things so differently that compatible code is impossible without big changes. Although standards are important to help bring some sort of commonality among the various RDBMSs’ implementation of SQL, at the end of the day what works in practice is what really counts. That said, the next section shows you how to create your own SQL database.
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