Relational database tables
In a relational database, we think of each dataset as a table, with each data point being a row in the table. The dataset's signature defines the columns of the table.
Here is an example of a relational database table. It has four rows and five columns, representing a dataset of four data points with five fields:
|
Last name |
First name |
Sex |
Age |
ID |
|---|---|---|---|---|
|
Adams |
John |
M |
26 |
704601929 |
|
White |
null |
F |
39 |
440163867 |
|
Jones |
Paul |
M |
49 |
602588410 |
|
Adams |
null |
F |
30 |
120096334 |
Note
There are two null fields in this table.
Because a database table is really a set of rows, the order of the rows is irrelevant, just as the order of the data points in any dataset is irrelevant. For the same reason, a database table may not contain duplicate rows and a dataset may not contain duplicate data points.
Key fields
A dataset may specify that all values of a designated field be unique. Such a field is called a key field for the dataset. In the preceding example, the ID number field...
