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Primary Keys Primary Keys comes the effectiveness of the relational database such as Microsoft Access from the ability to find information stored in separate tables quickly and assembled together using queries and forms and reports. To do so, we must Each table contains a field or group of fields you define every record store in the table is unique. This information is called the primary key for the table. When you set the primary key for the table, Access prevents the introduction of any duplicate values or Null values in the primary key fields. There are three types of primary keys that can be defined in Microsoft Access: the primary keys of type automatic numbering can be set up automatic numbering field to enter a serial number automatically when you add each record to the table. The simplest way to create a primary key is the appointment of such a field as the primary key. If you do not appoint a primary key table before saving the newly created, Microsoft stainless steel top dining table Access asks if you want to establish a primary key on your behalf. If you answered "yes", Microsoft Access stainless steel top dining table creates a primary key of type automatic numbering. Primary keys from a single field type if you have a field that contains unique stainless steel top dining table values, such as identification numbers or part numbers, you can set this field as a primary stainless steel top dining table key. It can identify a primary key field already contains data as long as that does not contain this field duplicate values or null values Null. The primary keys of the multi-field type in cases where you can not guarantee the existence of an individual field, you may be able to appoint two or more fields as the primary key. The most common case where there is a table that is used to link the two tables in the relationship of the parties other parties. stainless steel top dining table For example, a table can be linked to details of orders between tabular orders and products. It consists of its primary key fields: the definition of demand and product definition. A table that lists the order details many of the products and orders, but each product is listed once for each request, so it produces a collection of fields for the definition of demand and product identification primary key field appropriately. stainless steel top dining table If you have any doubt about the possibility of identifying a suitable installation of the fields for a multiple-field primary key, then maybe you should add AutoNumber field and set it as the primary key instead. stainless steel top dining table For example, the inclusion stainless steel top dining table of the fields "First Name" and "Last Name" to form a primary key is not a wise choice, because of the possibility of coincidence repeat included in these fields in the future. Set the primary key or change 1. Open the table in Design view. 2. Select the field or fields you want to define as the primary key. To select one field, click the row selector for the field that you want. To select multiple fields, stainless steel top dining table hold down the CTRL key and then click the row selector for each field. 3. Primary stainless steel top dining table key, click on the toolbar. Remove the primary key 1. When using the primary key in the relationship, the relationship must be deleted before you can remove the primary key. 2. Then open the table in Design view. 3. Click the row selector for the primary key, and then click the current primary key on the toolbar. Note This procedure does not delete the field or fields that are designated as the primary key, it simply removes stainless steel top dining table the features of the primary key of the table. Indexing fields and records in an Access database stainless steel top dining table index helps Microsoft Access to find and sort records stainless steel top dining table faster. And Access uses indexes on the table as the index used in the book in order to find the data, looking for the site where the data in the index. stainless steel top dining table You can create indexes based on a single field or multiple fields. Fields and indexes enable you to distinguish between multiple records that may contain the first field of which the same value. stainless steel top dining table Identify the fields that are indexed may need to index the fields that are looking for frequent or fields that are sort them or fields that are Bosslha fields in other tables in queries. However, the indexes may slow down some queries such as append query, when you need to update the indexes for a number of fields during the implementation of these processes. Is indexed table's primary key automatically, and you can not indexed field when the data type is an object OLE. For other fields, you should consider indexing field when the following applies it to: be the field's data type "text" or "No" or "currency" or "Date / Time". Find expect the values stored in the field. Sort expect the values stored in the field. expects the store several different values in the field. If several identical values in the field, it does not index to speed up queries significantly. Multiple-field indexes if you think you will be searching or sorting repeatedly stainless steel top dining table by two or more fields at a time, you can create an index for this combination of fields. For example, if you set the standards for the fields "Last Name" and "First Name" stainless steel top dining table in the same query repeatedly, it makes sense to create a multiple-field index in both fields. When you sort a table by multiple-field index, Microsoft Access sorts first by the first field defined for the index. If there are records of duplicate values in the first field, Microsoft Access field is secreted by the second field defined for the index, and so on. You can include up to 10 fields in a multiple-field index. Create an index to search for and sort records faster can create indexes based on a single field or multiple fields. And enables you to behold