One to one relation

Basic database relations:

One to one relation definition:

Relation one to one exist when one value from database entitiy (table) can be assigned only to one value from other entitiy  in this database.

One to one relation example:

Let’s take some example of shool database which contains 2 entities: Teachers (this table presents data about teachers employed at our example school) and Lessons (Lessons table shows  which teacher is responsible for specific lesson).

We suppose also that one teacher is responsible only for one lesson which means that each lesson can be conducted only by one teacher (conductiong this lesson  by another teacher is forbidden).

Relation one to one

As we can see in the above picture, between Teachers and Lessons tables exist one to one relation because one teacher (for example: Jack Smith) can be assigned only to one (as in the example with Jack Smith: Mathematics) lesson (one teacher is responsible for one lesson).

Relation one to one

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