An integral part of most database tables is the "Counter" field. What is the peculiarity of this column, what functions it performs and what properties it has, we will consider below. To do this, let us dwell in more detail on the concepts of databases, their objects and, in particular, tables, the element of which is the counter.

Database

Let's take a short excursion into database informatics. DB is a set of tables with information between which there are links. Databases are convenient for storing large amounts of data related to one topic. Business uses databases to store information about customers: names, dates of birth, address, passport and other personal data.

For each of the customers, a record of orders is kept: goods and their quantity, dates, delivery method, and other features. The information itself about the goods is also contained in the storages and is a complete set of parameters that characterize the products for sale.

Banks store in their information about customers, deposits and loans. It also contains financial parameters that allow you to generate reports for business analysis and submission to regulatory authorities.

A travel company works with a database that stores data about business partners, tourists, hotels and excursions. With the help of special applications, tariffs and cost of tours are calculated.

Thus, the data contained in the database correspond to the industry in which the company operates.

Database objects

The main object of the database is a table, the main storage of database information. These are the tables that we are used to seeing in the classroom at school or university, in books and textbooks. They are made up of rows, which are called records or tuples in databases, and columns called fields.

Queries perform the main work on the interaction of interface forms with other database objects, their elements and the base itself. When you simply click the Delete Row button on the database application form, it is the request that completes the action and fulfills your request.

Reports are used to output information to the printer, and macros and modules are provided in the database application interface to execute procedures in response to events.

Features of DB tables

As we know from the computer science course, databases are made up of tables. Each line contains data related to one object. Let's give an example. The database of the travel agency contains a table "Hotels", each record of which contains complete information on one of the hotels: name, category, address, website link, phone and fax number, etc.

Each of the columns determines which values \u200b\u200bare in it. From the same example of hotels, you can see that one of the fields is named "Name", and it contains only the names of hotels. Another field is the category, here it is written how many stars this hotel has. Thus, going through the entire column, we see the values \u200b\u200bof one parameter for each of the rows.

Database fields are of different types: text, numeric, currency, boolean, date and time format. This defines the constraints that are placed on the values \u200b\u200bin these columns. Having defined the type of the field "Date and time", we will no longer be able to enter the surname or first name into it, it is prohibited to enter alphabetic characters in a numeric field, and a value cannot be entered into a logical column.

The field type "Counter" stands apart. What is the peculiarity of its use, we will consider below.

Field of type "Counter"

Let's go back to our table of hotels. In the first column, which is called "Code", we see numbers - the serial numbers of each of the hotels. They are not repeated and indicate the record in such a way that we know exactly under which number a particular hotel is contained in the table. This makes it easy to find the hotel you want using this code.

The Code field is of the Counter type. What is the peculiarity of this field, based on the information above? First of all, it is the uniqueness of the column values. This property ensures that the record is uniquely identified. There cannot be two records in the table with the same value of the "Code" parameter. The uniqueness of the field values \u200b\u200ballows it to be used as a primary key, that is, a column that is referenced by fields in other tables.

Another feature of the counter is auto-increment - the property of automatic number increment. Thanks to it, the user does not need to think about what number to enter for the next entry. The system will itself increase the number of the previous one and assign this number to the new one.

Example

The "Hotels" table has been added to our experimental Access database. The field-counter is called "Code", the numbering starts from one.

The second table of the database - "Regions" - also contains a counter field. What is special about the region table? The fact that its records are used by the hotel table to specify the hotel location. Here the value is selected from the dropdown:

And by region we can see the hotels located there:

Thus, the counter field is a significant element of database tables that allows you to uniquely identify a record, automatically assign a unique number to it and then use this number when referring to object rows from another table.

For the first time, electricity metering devices appeared in the 19th century. Their appearance was associated with the massive research of electromagnetism carried out by scientists and their inventions, powered by electricity. Infrastructure development and disputes over the choice of DC or AC for the consumer led to the discovery of the transformer, and attempts to account for AC electrical energy have fueled disruptive innovations. In 1888, Oliver B. Schellenberger developed the first AC meter.

The principle of operation and device of the electricity meter

To make metering of active AC electricity, induction single-phase and three-phase devices are needed, and to meter direct current, which is used in electric transport, railways, etc. - electrodynamic counter.

The counting disk mechanism of the electric meter registers the number of revolutions of its moving part, which is proportional to the amount of electricity consumed.

In an induction electric meter, an aluminum disk (the moving part of the device), when electricity is consumed, rotates with the help of eddy currents, which are induced by the magnetic field of the meter coil. This is where the interaction of two fields occurs: the magnetic field of the eddy currents and the magnetic field of the coil. The meter is designed so that two currents are created for its operation, one of which flows in the circuit, parallel to the load, and the other in the circuit of the load current itself. Both of these currents flow in coils that are worn over iron cores. Their names are appropriate: "ampere coil" and "voltaic coil". The iron cores of the coils are magnetized by alternating current. The use of alternating electric current contributes to the fact that the poles of the electromagnets are constantly changing. This creates the effect of passing a magnetic field between them. The arrangement of the coils and the magnetic field between them is calculated so that they form eddy currents in the body of the disk, and the direction of these currents will induce the magnetic field to pull the disk along with it, creating rotation. The speed of rotation of the disk will be proportional to the magnitude of the currents in both coils, that is, the speed of rotation, based on practical calculations, will be directly proportional to the product of the cosine of the phase shift (power consumption) and voltage U and current strength I. Using simple connecting techniques from mechanics, the disk that rotates is associated with the digital readings of the instrument. The principle of operation of an electronic counter is that voltage and alternating current affect solid-state (electronic) elements, which leads to the creation of pulses at the output. The number of these pulses is proportional to the energy to be measured.

Types of electricity meters and their classification

There are several types and types of electricity meters, which differ in the type of measured values, design and type of connection. The meters are divided into devices that are directly connected to the power circuit and devices that are connected to the power circuit using special measuring transformers.

By design type, electricity meters are divided into:

1. An induction (electromechanical) meter is an electric meter in which a moving element made of a conductive material is affected by a magnetic field created by stationary conductive coils. The disk acts as a movable element. The magnetic field of the coils induces currents that flow through the disc. The amount of energy consumed is directly proportional to the number of revolutions of this disc.
2. An electronic (static) meter is an electric meter whose solid-state (electronic) elements are exposed to alternating current and voltage, which creates pulses at the output, the number of which is equal to the amount of measured energy. In such meters, the measurement of active energy is based on the fact that analog input signals of current and voltage are converted into a counting pulse.
3. A hybrid electricity meter is a middle ground between devices with a digital interface and a measuring electronic or induction part, with a mechanical calculating device. Such devices are rarely found.

The meters can also be classified according to the measured values: single-phase - they measure alternating current of 220 volts, 50 Hz, as well as three-phase, designed to measure voltage of 380 V and a frequency of 50 Hz. In high-voltage circuits, where the voltage reaches 600 V, are used three-phase meters with current transformers that measure electricity at 100 V.

What is the peculiarity of the counter data type

At present, electricity is accounted for mainly at one tariff. In this case, the cost of electricity is the same and does not depend on the time of its consumption. When establishing induction meter electricity readings are reproduced using mechanical parts. This mechanical data type has a certain degree of error, which affects payment for electricity ... Unlike induction meters, which do not allow multi-tariff electricity metering, electronic meters provide such an opportunity.

The calibration period for electronic electricity meters is 4 to 16 years.

In electronic meters, all readings are displayed on a liquid crystal display and have a digital data type, which practically negates all errors associated with mechanical influences on the parts of the device. Electronic meters will be an excellent solution for apartments with high energy consumption, as well as for businesses.

Electronic and mechanical household electricity meters

Household induction (mechanical) meters of electrical energy, due to a number of shortcomings, are being ousted from the market by electronic meters. Mechanical electricity meters are used in apartments where energy consumption is low.

Cons of induction meters:

• Inability to count more than one tariff;
• Lack of automatic reading function remotely;
• Significant degree of accounting error;
• Poor security against electricity theft;
• Operating and installation inconveniences;
• Low functionality.

The advantages of electronic meters include the ability to account for electricity at rates that are differentiated. That is, one-, two-, three-tariff and more meters have the ability to memorize and show the amount of consumed electricity, taking into account the time periods that are programmed in them. Such multi-tariff metering is implemented using a set of calculating mechanisms operating in established time intervals corresponding to different tariffs.

The principle of operation and the device of the electricity meter (video)

In the modern design of electrical systems, only electronic meters are used, because they have unlimited possibilities in terms of service and are the undisputed leaders in the "information" aspect.

\u003e\u003e Informatics 11th grade \u003e\u003e Informatics: Forums and їkh priznachennya. Robot rules at forums.

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DATABASE

TEST

1. The database is:

1. a set of data organized according to certain rules;
2. a set of programs for storing and processing large amounts of information;
3. an interface that supports filling and manipulating data;
4. a certain set of information.

2. The most common in practice are:

1. distributed databases;
2. hierarchical databases;
3. network databases;
4. relational databases.

3. The most accurate analogue of a relational database can be:

1. an unordered set of data;
2. vector;
3. family tree;
4. two-dimensional table.

4. Tables in databases are intended:

1. for storing database data;

5. to perform complex program actions.

5. Which of the following is not an Access object:

1.modules;
2. tables;
3. macros;
4. keys;
5. forms;
6. reports;
7. requests?

6. What are the requests for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex program actions;
6. to output the processed database data to the printer?

7. What are the forms for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;

8. What the modules are for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex program actions?

9. What macros are for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex program actions?

10. In what mode does the user work with the database:

1. in the design;
2. amateur;
3. in the given;
4. in operation?

11. In which dialog box the links between the fields of the database tables are created:

1.link table;
2. connection diagram;
3. data schema;
4.data table?

12. Why, when closing the table, Access does not offer to save the entered data:

1. flaw in the program;
2. because the data is saved immediately after entering the table;
3. because the data is only saved after the entire database is closed?

13. Without which objects the database cannot exist:

1.without modules;
2. no reports;
3. without tables;
4. without forms;
5. without macros;
6.without requests?

14. In which elements of the table are database data stored:

1.in the fields;
2. in lines;
3. in columns;
4. in records;
5.in cells?

15. Does the table contain any information, in which there are no records?

1. an empty table does not contain any information;
2. an empty table contains information about the structure of the database;
3. an empty table contains information about future entries;
4. a table cannot exist without records.

16. Does a table with no fields contain any information?

1.contains information about the structure of the database;
2. does not contain any information;
3. a table without fields cannot exist;
4. Contains information about future entries.

17. What is the peculiarity of the "counter" field?

18. What is the peculiarity of the "memo" field?

1. serves to enter numerical data;
2. serves to enter real numbers;
3. the data is not stored in the field, but in another place, and the field only stores a pointer to where the text is located;
4. has a limited size;
5. Has the property of automatic build-up.

1. a field whose values \u200b\u200bcannot be repeated;
2. a field that has a unique name;
3. field, the value of which has the property of building up.

20. Search keys in database management systems (DBMS) are:

1. range of records of the database file in which the search is carried out;
2. logical expressions that define search conditions;
3. fields by value of which the search is carried out;
4. numbers of records that match the search conditions;
5. the number of the first record that matches the search criteria?

KEY

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Nominated by the teacher of informatics of the Specialized School No. 252 of the Obolonsky District of the metro station Kiev Zhitinskoy O.I.

Informatics for 11 classes, download free of charge, plan notes in lessons, get ready to school

»[Teacher] [Tests] [Databases]

DATABASE

TEST

1. The database is:

1. a set of data organized according to certain rules;
2. a set of programs for storing and processing large amounts of information;
3. an interface that supports filling and manipulating data;
4. a certain set of information.

2. The most common in practice are:

1. distributed databases;
2. hierarchical databases;
3. network databases;
4. relational databases.

3. The most accurate analogue of a relational database can be:

1. unordered data set;
2. vector;
3. family tree;
4. two-dimensional table.

4. Tables in databases are intended:

1. for storing database data;
2. to perform complex program actions.

5. Which of the following is not an Access object:

1. modules;
2. tables;
3. macros;
4. keys;
5. forms;
6. reports;
7. requests?

6. What are the requests for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex program actions;
6. to output the processed database data to a printer?

7. What are the forms for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex programming actions?

9. What macros are for:

1. for storing database data;
2. for selection and processing of database data;
3. to enter database data and view them;
4. to automatically execute a group of commands;
5. to perform complex programming actions?

10. In what mode does the user work with the database:

1. in the design;
2. in the amateur;
3. in the given;
4. in exploitation?

11. In which dialog box the links between the fields of the database tables are created:

1. link table;
2. connection diagram;
3. data schema;
4. data table?

12. Why, when closing the table, Access does not offer to save the entered data:

1. flaw in the program;
2. because the data is saved immediately after entering the table;
3. because the data is only saved after the entire database is closed?

13. Without which objects the database cannot exist:

1. without modules;
2. no reports;
3. no tables;
4. without forms;
5. no macros;
6. without requests?

14. In which elements of the table are database data stored:

1. in the fields;
2. in lines;
3. in columns;
4. in records;
5. in cells?

15. Does the table contain any information, in which there are no records?

1. an empty table does not contain any information;
2. an empty table contains information about the structure of the database;
3. an empty table contains information about future entries;
4. a table without records cannot exist.

16. Does the table with no fields contain any information?

1. contains information about the structure of the database;
2. does not contain any information;
3. a table without fields cannot exist;
4. contains information about future entries.

17. What is the peculiarity of the "counter" field?

1. has a limited size;

18. What is the peculiarity of the "memo" field?

1. serves to enter numerical data;
2. serves to enter real numbers;
3. data is not stored in the field, but in another place, and the field only stores a pointer to where the text is located;
4. has a limited size;
5. has the property of automatic building.

1. a field whose values \u200b\u200bcannot be repeated;
2. a field that has a unique name;
3. field, the value of which has the property of building.

20. Search keys in database management systems (DBMS) are:

1. the range of records of the database file in which the search is performed;
2. logical expressions that define search conditions;
3. fields by value of which the search is performed;
4. numbers of records that match the search conditions;
5. the number of the first record that matches the search conditions?

KEY