Database

Databases are a collection of data stored in a long-term computer memory and allowing certain ways of searching for information. In the form of databases, various information can be stored: the timetable for the movement of trains, buses and planes, information about the availability of goods in the store or in the warehouse, information about students, teachers and employees, information about books and much, much more.

Databases are a collection of data stored in a long-term computer memory and allowing certain ways of searching for information

Databases can be organized in several ways. The tabular form is the simplest and most widespread form of organization, called the relational one. Example of the table:

Surname Name Growth Weight Eyes
Ivanov Sasha 180 85 blue
Petrova Olga 165 65 brown
Toropov Misha 185 75 green

Relational databases are databases in which information is stored in the form of tables. Each of the tables of such a database has a strictly defined number of columns, provided with names. In each column, data of a certain type can be written-numeric or symbolic.

The most important feature of the database is the automatic retrieval of information. The basis for searching database information is the query.

Database queries are divided into simple and complex. In simple queries, you specify the name of one of the columns and a certain value. Examples of simple queries:

Request: Surname = Ivanov

Request: name = Olya

The answers to the database queries will be the rows from the table of this type. For numeric values in queries, the signs "more" or "less" may be. Examples of related queries:

Query: growth> 180

Request: weight≤ 50

The answers to these requests will also be one or more rows from the table, in which the height or weight will satisfy the specified conditions.

Complex database queries are formed from the simplest ones using logical connectives and and or. Examples of compound queries:

Request: weight< 80 and eyes = green

Request: eyes = blue or eyes = blue

Responses to compound queries with a database bundle and will be all rows of the table that satisfy both conditions. Responses to queries with a binder or will be all rows of the table that satisfy the first or second condition, or both at the same time.

The difference between the database and information and information retrieval systems is as follows. In information and reference systems, only information retrieval is allowed. And databases do not only search for information, but also update it, and create new tables.

Updating the database in the tables is carried out by the elements of the rows, and the addition of information - by entering new rows. To create a new table, you must specify its name, the number of columns, and specify the types of values in each column.

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