Adelphia web hosting - In this chapter, you learn about the following:
In this chapter, you learn about the following: . What SQL is . The origins of SQL . Many types of queries . Changing data in tables . Changing table structure Defining SQL SQL is a non-procedural language used for accessing field and record values in relational database tables. A procedural programming language is a language where there can be dependencies between sequential commands. For example, when setting a variable X = 1 on a line, that variable X can be used to reference the value 1, as the variable X in subsequent lines of programming code. A non-procedural programming language does not allow communication between different lines of programming code. Non-procedural languages also do not allow use of procedures. A procedure allows intra-program communication by passing values in and out of procedures. Keep in mind the following when considering what SQL is. . SQL is structured in the sense that it is used to access structured data, in a structured manner, or retrieve data from organized structures. Those organized structures are tables. . Use of the word language implies a computer programming language. Computer programming languages are often used to get information from a computer. . A non-procedural language essentially submits a single command, with a questioning or querying type nature. SQL is a non-procedural language consisting of single commands, where the database itself does a lot of the work in deciding how to get that information. On the other hand, a procedural language contains blocks of commands. Those blocks of commands are sequences of distinct steps, typically where each successive step is dependent on the result of the previous command in the sequence. . In most relational databases, SQL does have the capability to function in a limited procedural fashion, allowing the programmer to determine partially how a database is accessed. Traditionally, SQL procedural code is used to write what are called stored procedures, triggers, database events, or database procedures. There are other names for these code blocks, depending on the database in use. Procedural SQL code is generally simplistic and can sometimes allow the inclusion of basic programming constructs such as IF statements, CASE statements, and so on. So, SQL is a simple non-procedural programming language allowing single line commands. These singleline commands are used to access data stored in database table structures. 124 Chapter 5
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