When selecting a primary key from among the candidate keys, choose the one that contains the least number of fields, and secondarily, is most closely associated with the subject of the table. To summarize, the characteristics of a primary key field or fields are that. Some RDBMS 's have the capability and a data type to generate a unique number for you. Some tables may have multiple possibilities for the primary key. Each of these is called a candidate key. You want to use the fewest fields possible that satisfy these criteria. Following is an example of a table with a multi-field primary key-the fields included in the primary key are indicated by an asterisk. Primary keys set unique column identifiers for your Oracle tables. Primary keys are assigned during the design phase of database tables, and. How Do I Create a Custom Primary Key in Microsoft Access? If desired, you can edit the data so it's no longer duplicated. Tips Warnings. Windows users can select multiple fields by holding the Control key and then clicking in each field to be used. Room Date StartTime EndTime Purpose A 1:00 PM 3:00 PM. Staff Meeting A 4:00 PM 5:00 PM Dept. Managers B 9:00 AM 10:30 AM. STAR Project B 1:00 PM 5:00 PM Proposal Presentation C 9:00 AM 10:00 AM Staff Meeting Above, an example of a. In most RDBMS 's, the records in a table are automatically in order by the values in the primary key. But you don't care what order the records are in! Why don't you care? This field or fields are called the primary key of the table. The primary key serves several purposes in a RDBMS. Because the value is unique, it ensures there are no duplicate records in the database. For example, in a table holding information on orders placed with a company, there would be a field with a unique number for each order. If there is no single field that meets the qualifications for a primary key, you can have a multi-field, compound.