Relational databases: field

The idea

In a relational database, a field is one column of a table that stores a single attribute for every record, such as CustomerID, Surname or Email. Each field has a defined data type and holds one piece of information about the entity. Within a single record, one field holds one value, for example the surname 'Patel'. A field is not the whole row (that is a record) and not the whole table. Fields define the structure of a table: every record in the table has the same set of fields. A field can also be a key, such as a primary key that uniquely identifies each record. Recognising a field as one attribute column is the skill tested here.

What earns the marks

• A field is a single column in a table storing one attribute.
• Each field has a defined data type, such as text, number or date.
• Every record in a table contains the same set of fields.
• A field can act as a key, for example a primary key that uniquely identifies a record.
• A field is not the whole row (a record) nor the whole table.

Common mistakes and how to put them right

• Confusing a field with a record.

  Put it right: A field is one attribute column, whereas a record is a whole row of fields.

• Thinking a field holds all the data about an entity.

  Put it right: It holds only one attribute of that entity.

• Assuming fields can vary between records in the same table.

  Put it right: All records share the same field structure.

Exam tips

• Look for the word 'column' or 'attribute' when identifying a field in a table diagram.
• Check the data type of a field to confirm it stores one kind of value.
• Eliminate options describing a whole row, because those describe a record, not a field.