Columns (Visual Database Tools)
In a table, data is arranged into columns. Each column stores one data element, such as a first name, one line of an address, a price, or any similar discrete unit of information. For more information, see Working with Columns.
When columns are created in a table, they are given a name that identifies their purpose, such as FirstName or Address1. In most databases, you must also specify additional properties, such as how long the longest entry in the column will be, and what type of data the column will contain - characters, integers, floating-point numbers, dates or times, and so on. Other column properties can include whether the column is the table's primary key, whether users must enter a value into it, and what its default value is.
Column Properties
Each column in a table has a set of properties. Each property defines one characteristic, such as the name, data type or length, of a column. The entire set of properties for a column makes up that column's definition in your database table.
You can set column properties in Table Designer. Two column properties are required — the column name and data type— before you can save a table in your database. If you don't choose a data type, a default one will be provided. You can redefine a column by editing any of its properties. For example, you can rename a column, alter its length, specify a default value, and so on.