The columns of the table define what kind of information we can store in a table. If we make a comparison between a table and an entity type (a C# class), then we can say that the table column is equivalent to a property of the entity. To define a property on a class, we have to give it a name and a data type. Similarly, a table column has a name and a data type. We can define even more characteristics on a column such as a restriction whether the column is nullable or not. By the way, null is a database term used to define an undefined value.
You might have already noticed that the data types used for table columns differ quite a bit from those you generally use when defining properties of a C# class. The only column data type that looks familiar so far is int. This is a fact we have to live with. It is even worse as every database product has its own specific types. Oracle column types are different from those of Microsoft SQL Server, which in turn...