When you create a table or add a field to a table in the geodatabase, fields are created as a specific data type. Data types are classifications that identify possible values for and operations that can be done on the data, as well as the way the data in that field is stored in the database.
When you import data of one type into a field of another data type, you need to understand what the equivalent data types are between ArcGIS and your database management system (DBMS), because it can impact data content. Also, when creating datasets in ArcGIS, it is helpful to know the equivalent data types between ArcGIS and your DBMS. For example, if you add a floating-point (float) column to an existing feature class, it equates to a numeric data type column in a Microsoft SQL Server database.
Moving data from one database to another can cause data types to remap.
File and mobile geodatabase data types are the same as ArcGIS data types. For DBMS products, though, data types can differ. See Data types supported in ArcGIS for information on how ArcGIS data types map to DBMS data types.