Each record in a database table corresponds to an entity. In the example table of 'Students' above there are 5 records. Each record corresponds to an individual student. Note that although there are two students called Mashiyat and Ahammed with the same date of birth, they have different Student IDs and are different students. Field: An attribute is a piece of information or a characteristic of an entity.
Attributes of entities are represented in database tables by fields columns. A field stores one item of data for a record. In the table above, each student is represented in the database by a record and the student attributes are stored in the following fields:. Primary Key: A primary key is a unique field. That means the data in this field is different for every record in the data table. Consider a teacher who keeps records of students.
Student name is not a primary key because you could have two students with the same name. Date of birth is not a primary key, because two students could have the same birthday. For this reasons the teacher might give every student a code number Student ID.
The number given to each student would be unique to that student. The records would never get mixed up. The primary key is whatever field is used to identify each record in the database. Having a primary key is even more important in a big data table. For example, a bank database. A data type is a format that we can give to data in a field. When entering data into a database we need to consider the appropriate data type for each field. The data type of a field will depend on the data that is being stored in the field.
Character data type : It can store no more than one text character. Databases can be very useful for searching through data. A search in a database is known as query. A query is a computer command that picks out only the records and fields that you want to see. A query-by-example is a method of making a query. In a query-by-example we choose each field we want to appear in the results and set any criteria we want to apply to that field. The criteria can be chosen using one or more of several operators , shown in table below.
Tag Archive Tag Archives for " Computer science ". What is data transmission? Data transmission is used to link computers. The computers can share and send data. The internet is based on long distance communication links. Data transmission is also used over short distances.
The different parts of a computer transmit data to each other. When you send your work to a printer that requires data transmission.
Bluetooth is an example of a short distance wireless link. Essentially, three factors need to be considered when transmitting data. The direction of the data transmission How many bits are sent at the same time The method of synchronization between the devices.
Simplex Data is sent in one direction only in simplex transmission. Half-Duplex Half-duplex transmission , data is sent in both directions but only one direction at a time. Full-duplex In full duplex transmission mode, the communication between sender and receiver can occur simultaneously. How many bits are sent at the same time? Serial transmission Most data transmission is serial transmission. Parallel transmission Parallel transmission uses several wires to transfer the data bits simultaneously.
What is database? Data and Information Data is a collective term for facts and figures. Database can be used in different ways, for example: In schools, databases can store data about students such as their name, address, date of birth, admission date and ID. They could store attendance registers. They could also be used by teachers to record exam results. Patient medical records held at a hospital are used by doctors and nurses to help treat patients.
Search engines store data about websites. Such as their name, web address and content. User can quickly search for and find the information about any website they are looking for. Advantages of database: The data can easily be stored in a specific way.
The data we need can be found quickly. Data can easily be shared over the internet or using a portable storage device. Data can be validated to make sure that data entered is possible, realistic and sensible. Data can be filtered to retrieve only the data we require. Secure Remote Workforce During Coronavirus. Learn more on how to stay protected from the latest Ransomware Pandemic.
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