CheckConnection that the connection to the database is available.

Connect to the database.

FloatToNull is a function to convert a float to a sql.NullFloat64.

InitDB is the function that initializes the database.

IntToNull is a function to convert a int to a sql.NullInt64.

MakeMigration creates the tables.

NewConnection is the function to get only connection.

StringToNull is a function to convert a string to a sql.NullString.

CardStorage is the interface that wraps the methods to manage the cards.

Data manages the connection to the database.

EmployeeTypeStorage is the struct that contains the database connection.