One-to-one relationships are an essential part of building a database
A one-to-one relationship occurs when there is exactly one item in the first table that matches one item in the related table. For example, US citizens have a Social Security number. Only one number is assigned per person, so a person cannot have multiple numbers.
Here’s another example using the two tables below. The tables have a one-to-one relationship because each row in the first table is directly related to another row in the second table.
Personnel number td>
Last name td>
So the number of rows in the table with the employee’s name must match the number of rows in the table with the employee’s title.
personnel number td>
Another type of database model is the one-to-many relationship. From the table below, you can see that Rob Halford is a manager, so his relationship to the position is unambiguous as there is only one position in this company. But the manager position includes two people, Amy Bond and Rob Halford, who have a one-to-many relationship. One position, many people.
Learn more about database relationships, foreign keys, joins, and ER diagrams.
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