Tables are grids that store information in a database similar to the way an Excel worksheet stores information in a workbook. Access provides three ways to create a table for which there are icons in the Database Window. Double-click on the icons to create a table.
Create table in Design view will allow you to create the fields of the table. This is the most common way of creating a table and is explained in detail below.
Create table using wizard will step you through the creation of a table.
Create table by entering data will give you a blank datasheet with unlabelled columns that looks much like an Excel worksheet. Enter data into the cells and click the Save button. You will be prompted to add a primary key field.
After the table is saved, the empty cells of the datasheet are trimmed. The fields are given generic names such as "Field1", "Field2", etc. To rename them with more descriptive titles that reflect the content of the fields, select Format|Rename Column from the menu bar or highlight the column, right-click on it with the mouse, and select Rename Column from the shortcut menu.
Design View will allow you to define the fields in the table before adding any data to the datasheet. The window is divided into two parts: a top pane for entering the field name, data type, and an option description of the field, and a bottom pane for specifying field properties.
Properties for each field are set from the bottom pane of the Design View window. Field Size is used to set the number of characters needed in a text or number field. The default field size for the text type is 50 characters. If the records in the field will only have two or three characters, you can change the size of the field to save disk space or prevent entry errors by limiting the number of characters allowed. Likewise, if the field will require more than 50 characters, enter a number up to 255. The field size is set in exact characters for Text type, but options are give for numbers:
Select one of the preset options from the drop down menu or construct a custom format using symbols explained below:
In the table below, the value "1/1/01" is entered into the datasheet, and the following values are displayed as a result of the different assigned formats.
Every record in a table must have a primary key that differentiates it from every other record in the table. In some cases, it is only necessary to designate an existing field as the primary key if you are certain that every record in the table will have a different value for that particular field. A social security number is an example of a record whose values will only appear once in a database table.
Designate the primary key field by right-clicking on the record and selection Primary Key from the shortcut menu or select Edit|Primary Key from the menu bar. The primary key field will be noted with a key image to the left. To remove a primary key, repeat one of these steps.
If none of the existing fields in the table will produce unique values for every record, a separate field must be added. Access will prompt you to create this type of field at the beginning of the table the first time you save the table and a primary key field has not been assigned. The field is named "ID" and the data type is "autonumber". Since this extra field serves no purpose to you as the user, the autonumber type automatically updates whenever a record is added so there is no extra work on your part. You may also choose to hide this column in the datasheet as explained on a later page in this tutorial.
Creating indexes allows Access to query and sort records faster. To set an indexed field, select a field that is commonly searched and change the Indexed property to Yes (Duplicates OK) if multiple entries of the same data value are allowed or Yes (No Duplicates) to prevent duplicates.
Validation Rules specify requirements (change word) for the data entered in the worksheet. A customized message can be displayed to the user when data that violates the rule setting is entered. Click the expression builder ("...") button at the end of the Validation Rule box to write the validation rule. Examples of field validation rules include <> 0 to not allow zero values in the record, and ??? to only all data strings three characters in length.
An input mask controls the value of a record and sets it in a specific format. They are similar to the Format property, but instead display the format on the datasheet before the data is entered. For example, a telephone number field can formatted with an input mask to accept ten digits that are automatically formatted as "(555) 123-4567". The blank field would look like (___) ___-____. An input mask to a field by following these steps: