![]() ![]() In fact, the model does not describe in any way how the information is stored and accessed. The relational model made it possible to separate the particular features of data storage from the application layer. If the internal database structure was changed (for example, to increase the performance), it was necessary to recycle the application programs, even if there were no changes on the logical level. Prior to that, the specific features of storing information in the database had to be taken into account when using the database. It described a mathematical apparatus for data structuring and management, and proposed an abstract model to represent any real information. The concept of a relational model was first proposed in the paper by Dr. Without going into details, a relational DBMS is a system based on a relational data management model. The standard sql-92 does not even contain the term relation. However, you will soon see that there is a difference between them. Many even think that the expressions “a database processed by means of sql” and “relational database” are synonyms. The most essential property of sql is the ability to access relational databases. In other words, when working with sql, we are interested in the results, not in the procedures for obtaining them. It cannot be used to specify how a task is to be performed, but only to determine what it is. An auxiliary language is used only in combination with other languages.Ī general-purpose application language usually has tools for creating procedures, but not in sql. That’s why sql is also called an auxiliary language tool for data processing. Specialization means that sol is intended only for working with the database you cannot create a full-fledged application system by means of this language only – this requires using other languages in which you can embed sql commands. SQL is a specialized non-procedural language that allows you to describe data, select and process information from relational DBMS. This knowledge can become the basis for further independent development of sql. As a result, you will be able to create tables and enter information into them yourself, make queries and work with reports. In this article, we will take a look at the basic commands of sql, rules of setting criteria for data selection and show how to get results. As a tourist who finds himself in a country where people speak an incomprehensible language, it’s enough to learn only a few useful expressions and grammar rules, and in sql – knowing little, you can get many useful results. However, it is not necessary for an ordinary user to know sql completely. ![]() The language is so developed and diverse that only a simple enumeration of its features will require several journal articles, and if you collect everything written on the subject of sol, you will get a multi-volume library. The text of the current standard – the official document “the international standard database language SQL” (usually called sql-92) – contains more than six hundred pages, but it does not say anything about the specific features of the versions of sol, implemented in the DBMS firms microsoft, oracle, sybase and others. sql was introduced in 1974 as a small 23-page research paper and has come a long way since then. In order to become a professional you will have to learn a lot. Is it hard to learn SQL? It depends on how deeply you are going to get to the bottom of it. You will get acquainted with the relational model and will be able to acquire the first skills of working with sql, which will help you further master the language. We will tell its prehistory (and dispel several myths along the way). ![]() In this article we will consider the basic concepts of SQL.
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