meaning of query in database
This article provides a brief overview of databases — what they are, why you might want to use one, and what the different parts of a database do. The terminology is geared toward Microsoft Access databases, but the concepts apply to all database products.
What is a database?
A database is a tool for collecting and organizing information. Databases can store information about people, products, orders, or anything else. Many databases start as a list in a word-processing program or spreadsheet. As the list grows bigger, redundancies and inconsistencies begin to appear in the data. The data becomes hard to understand in list form, and there are limited ways of searching or pulling subsets of data out for review. Once these problems start to appear, it's a good idea to transfer the data to a database created by a database management system (DBMS), such as Access.
A computerized database is a container of objects. One database can contain more than one table. For example, an inventory tracking system that uses three tables is not three databases, but one database that contains three tables. Unless it has been specifically designed to use data or code from another source, an Access database stores its tables in a single file, along with other objects, such as forms, reports, macros, and modules. Databases created in the Access 2007 format (which is also used by Access, 2016, Access 2013 and Access 2010) have the file extension .accdb, and databases created in earlier Access formats have the file extension .mdb. You can use Access 2016, Access 2013, Access 2010, or Access 2007 to create files in earlier file formats (for example, Access 2000 and Access 2002-2003).
Using Access, you can:
- Add new data to a database, such as a new item in an inventory
- Edit existing data in the database, such as changing the current location of an item
- Delete information, perhaps if an item is sold or discarded
- Organize and view the data in different ways
- Share the data with others via reports, e-mail messages, an intranet, or the Internet
The parts of an Access database
The following sections are short descriptions of the parts of a typical Access database.
A database table is similar in appearance to a spreadsheet, in that data is stored in rows and columns. As a result, it is usually quite easy to import a spreadsheet into a database table. The main difference between storing your data in a spreadsheet and storing it in a database is in how the data is organized.
To get the most flexibility out of a database, the data needs to be organized into tables so that redundancies don't occur. For example, if you're storing information about employees, each employee should only need to be entered once in a table that is set up just to hold employee data. Data about products will be stored in its own table, and data about branch offices will be stored in another table. This process is called normalization.
Each row in a table is referred to as a record. Records are where the individual pieces of information are stored. Each record consists of one or more fields. Fields correspond to the columns in the table. For example, you might have a table named "Employees" where each record (row) contains information about a different employee, and each field (column) contains a different type of information, such as first name, last name, address, and so on. Fields must be designated as a certain data type, whether it's text, date or time, number, or some other type.
Another way to describe records and fields is to visualize a library's old-style card catalog. Each card in the cabinet corresponds to a record in the database. Each piece of information on an individual card (author, title, and so on) corresponds to a field in the database.
Forms allow you to create a user interface in which you can enter and edit your data. Forms often contain command buttons and other controls that perform various tasks. You can create a database without using forms by simply editing your data in the table datasheets. However, most database users prefer to use forms for viewing, entering, and editing data in the tables.