Consistency Because each item of data is recorded only once, in one table, there is less opportunity for ambiguity or inconsistency. For example, you store a customer's name only once, in a table about customers, rather than storing it repeatedly and potentially inconsistently in a table that contains order data.
Efficiency Recording data in only one place means you use less disk space. Moreover, smaller tables tend to provide data more quickly than larger tables. Finally, if you don't use separate tables for separate subjects, you will introduce null values the absence of data and redundancy into your tables, both of which can waste space and impede performance.
Comprehensibility The design of a database is easier to understand if the subjects are properly separated into tables. Plan your tables with relationships in mind. You can use the Lookup Wizard to create a foreign key field if the table that contains the corresponding primary key already exists.
The Lookup Wizard creates the relationship for you. For more information, see Create or delete a lookup field. Create a table and add fields. Creating tables. Need more help? Expand your skills. Get new features first. Was this information helpful? Yes No. Thank you! Any more feedback?
The more you tell us the more we can help. Can you help us improve? Resolved my issue. Clear instructions. Easy to follow. No jargon.
Pictures helped. Didn't match my screen. Incorrect instructions. Too technical. Not enough information. Not enough pictures. Any additional feedback? For example, a phone book has a last name, a first name, an address, and a phone number for each entry. Each entry in the telephone list has a unique identifying quality, which is the name of the person. Each entry by name in the phone book forms a row, containing unique data in each of these four columns. The databases are organized into fields and records to make them easy to access.
Most databases follow this basic organization and functional principles. As a rule, the database field refers to the columns, or categories of data, that are used by all entries or rows. A record is a row in a database, a horizontal grouping of data. The content of these fields is unique to that row.
In the phone book example, each last name begins a row or record that contains data in the first name, address, and phone number fields. A record is often used in a database search because each record has a unique identifying quality or value.
The field size defines the maximum number of characters a field can contain. For example, the Instructor ID field contains 6 characters and thus has a field size of 6. The type of data in a field is an important consideration. The image to your right identifies the data types for fields in the Instructor and Student files. The data type specifies the kind of data a field can contain and how the field is used.
Common data types include:. A record is a group of related fields. For example, the Student ID field uniquely identifies each student because no two students can have the same Student ID. In some tables, the primary key consists of multiple fields, called a composite key. For example, the primary key for the Schedule of Classes file could consist of the fields Semester Code, Class Code, and Class Section, which together would uniquely identify each class listed in a schedule.
Difference Between File and Database.
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