Primary Key

• A primary key, also called a primary keyword, is akey in a relational database that is unique for each record. It is a unique identifier, such as a driver license number, telephone number (including area code), or vehicle identification number (VIN). A relational database must always have one and only one primary key.
• A primary key field is an index that greatly speeds up queries, searches and sort requests.
• When you add new records, you must enter a value in the primary key field(s). Microsoft Access will not allow you to enter Null values, which guarantees that you will have only valid records in your table.
• When you add new records to a table that has a primary key, Microsoft Access checks for duplicate data and doesn't let you enter duplicates for the primary key field.
• By default, Access displays your data in the order of the primary key.
• Primary key fields should be made as short as possible as this can affect the speed of operations in the database.

Data types in MS Access

Every table in Access is made up of fields. The properties of a field describe the characteristics and behavior of data added to that field. A field's data type is the most important property because it determines what kind of data the field can store. This blog describes the data types and other field properties available in Access, and includes additional information in a detailed data type reference section.

Basic Types

Format	Use to display
Text	Short, alphanumeric values, such as a last name or a street address. Note, beginning in Access 2013, Text data types have been renamed to Short Text.
Number, Large Number	Numeric values, such as distances. Note that there is a separate data type for currency.
Currency	Monetary values.
Yes/No	Yes and No values and fields that contain only one of two values.
Date/Time	Date and Time values for the years 100 through 9999.
Rich Text	Text or combinations of text and numbers that can be formatted using color and font controls.
Calculated Field	Results of a calculation. The calculation must refer to other fields in the same table. You would use the Expression Builder to create the calculation. Note, Calculated fields were first introduced in Access 2010.
Attachment	Attached images, spreadsheet files, documents, charts, and other types of supported files to the records in your database, similar to attaching files to e-mail messages.
Hyperlink	Text or combinations of text and numbers stored as text and used as a hyperlink address.
Memo	Long blocks of text. A typical use of a Memo field would be a detailed product description. Note, beginning in Access 2013, Memo data types have been renamed to Long Text.
Lookup	Displays either a list of values that is retrieved from a table or query, or a set of values that you specified when you created the field. The Lookup Wizard starts and you can create a Lookup field. The data type of a Lookup field is either Text or Number, depending on the choices that you make in the wizard. Lookup fields have an additional set of field properties, which are located on the Lookup tab in the Field Properties pane.

https://support.office.com/en-us/article/Introduction-to-data-types-and-field-properties-30ad644f-946c-442e-8bd2-be067361987c

DATABASES

Nowadays, computers are used everywhere and some uses are like in offices,schools,hospitals,etc.

We often need to store huge amount of records in the places listed above.

For this we require various softwares which are called DBMS(Database Management System).A DBMS is a computer software application that interacts with the user, other applications, and the database itself to capture and analyze data. A general-purpose DBMS is designed to allow the definition, creation, querying, update, and administration of databases.
Some DBMS examples include MySQL, PostgreSQL, Microsoft Access, SQL Server, FileMaker, Oracle, RDBMS, dBASE, Clipper, and FoxPro.

There are four structural types of database management systems:

• Hierarchical databases.
• Network databases.
• Relational databases.
• Object-oriented databases.