Data Types of Fields and Field Size
Before creating a database, you must know the data type of field and the field size. The field size specifies the maximum number of characters or amount of data that can be stored into the field. Similarly, different types of data can be stored into fields of record. It may be text type, numeric type or date type etc. Therefore, the data type specifies the type of data a field can store (or contain).
The most common data types of fields used in Microsoft Access are described below.
Text Field – It is – used to store characters, numbers, special characters etc. The arithmetic operations can not be performed on text data type field. These fields are used to store names of persons, addresses, telephone numbers etc. The maximum size of text field is 255 characters. The default setting is 50 characters.
Numeric Field – It is used to store numeric data. The arithmetic operations can be performed on these data type fields. In numeric data fields, the whole numbers and real or floating numbers can be stored. For example, to store N an amount or student’s subject marks, this numeric data type field is used.
Date & Time Field – It is used to store date or time entries. This type of field converts the value of date or time into numeric value. It is because the arithmetic calculations can be performed on this data type field. For example, to store the date of birth, date of joining of an employee etc. the data type of field is declared as date & time.
Memo Field – It is like text field but it is used to store large amount of text. For example, comments or descriptions are stored into this type fields.
Hyper Link – It is used to store the hyper links or links of the web page For example, “http://www.free-computer-tips.info” is a web page address.
Object Field – It is used to store the picture, audio video or a document created in another application program.
Logical Field – It is used to store true/yes or false/no value. For example in a student table, the result field is defined to store value “True” if student is pass and value “False” is student is fail.
Logical Field – It is used to store true/yes or false/no value. For example in a student table, the result field is defined to store value “True” if student is pass and value “False” is student is fail.
Primary Key
A primary key for a table is a field (or a group of fields) with the property that no two records of a table contain the same value in that field or group of fields. It means that a primary key uniquely identifies a record in its table. For example, .the Roll numbers allotted to students in a class are unique and no two records or rows can contain the same value in the Roll number field in the student table. Therefore, you can set the Roll number field as the primary key. On the other hand, the Name field cannot be set as primary key because more than one students can have the same name.
