Key,+Primary+key,+Secondary+Key,+Data+types

Key, Primary key, Secondary Key, Data types

Keys are crucial to a table structure for many reasons, some of which are identified below: The primary key of a relational table uniquely identifies each record in the table. Example: Imagine we have a STUDENTS table that contains a record for each student at a university. The student's unique student ID number would be a good choice for a primary key in the STUDENTS table. The student's first and last name would not be a good choice, as there is always the chance that more than one student might have the same name. 10 types are.. Sometimes, the data in a field may appear to be one data type, but is actually another. For example, a field may seem to contain numeric values but may actually contain text values, such as room numbers. You can often use an expression to compare or convert values of different data types. **Byte ** — Use for integers that range from 0 to 255. Storage requirement is 1 byte. **Integer ** — Use for integers that range from -32,768 to **32,767**. Storage requirement is 2 bytes. **Long Integer ** — Use for integers that range from -2,147,483,648 to 2,147,483,647. Storage requirement is 4 bytes. **Single ** Use for numeric floating point values that range from -3.4 x 1038 to 3.4 x 1038 and up to seven significant digits. Storage requirement is 4 bytes. **Double ** Use for numeric floating point values that range from -1.797 x 10308 to 1.797 x 10308 and up to fifteen significant digits. Storage requirement is 8 bytes. **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">Replication ID **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;"> Use for storing a globally unique identifier required for replication. Storage requirement is 16 bytes. Note that replication is not supported using the .accdb file format. **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">Decimal **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;"> Use for numeric values that range from -9.999... x 1027 to 9.999... x 1027. Storage requirement is 12 bytes.
 * <span style="color: red; font-family: 'Verdana','sans-serif'; font-size: 24px;">Key Fields **
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">They ensure that each record in a table is precisely identified.
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">They help establish and enforce various types of integrity.
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">They serve to establish table relationships.
 * <span style="color: red; font-family: 'Verdana','sans-serif'; font-size: 24px;">Primary Key **
 * <span style="color: red; font-family: 'Verdana','sans-serif'; font-size: 24px;">Secondary Key **
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">A key that holds the physical location of a record or a portion of a record in a file or database, and provides an alternative means of accessing data. Also known as alternate key.
 * <span style="color: red; font-family: 'Verdana','sans-serif'; font-size: 24px;">Key Fields **
 * <span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Think of a field's data type as a set of qualities that applies to all the values contained in the field and that determines what kind of data those values can be. For example, values that are stored in a Text field can contain only letters, numbers, and a limited set of punctuation characters. In addition, a Text field can contain a maximum of 255 characters.
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Attachment **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> Files, such as digital photos. Multiple files can be attached per record. This data type is not available in earlier versions of Access.
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">AutoNumber **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> Numbers that are automatically generated for each record.
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Currency **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Monetary Values
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Date/Time **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Dates and times
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Hyperlink **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> Hyperlinks such as e-mail addresses
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Memo **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> Long blocks of text and text that use text formatting. A typical use of a Memo Field would be a detailed product description
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Number **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Numeric values, such as distances. Note that there is a separate data type for currency
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">OLE object **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">OLE objects such as word documents
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Text **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> Short alphanumeric values, such as a last name or street address
 * **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;">Yes/No **<span style="font-family: 'Verdana','sans-serif'; font-size: 16px;"> boolean values
 * **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">Field Size ** || <span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">Select one of the following:
 * <span style="font-family: 'Tahoma','sans-serif'; font-size: 8px;">Tip **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">Use **Long Integer** when you create a foreign key to relate to another table's AutoNumber primary key field.
 * <span style="font-family: 'Tahoma','sans-serif'; font-size: 8px;">Tip **<span style="font-family: 'Tahoma','sans-serif'; font-size: 10px;">For best performance, always specify the smallest sufficient **Field Size**. ||