good morning the reason for my question is more informative is about the space that occupies a field null in the database, since I have a database with several fields and sometimes I have several fields in null and I worries about the space this null field can have in my database, since I do not want to waste the memory of my server when implementing the database, when I consult about the information on the subject I find a lot of contradictory information I would like to know where you can find reliable information on the subject, also I'm using Mysql as a database engine
I have attached an example of my database 
I'm not very good with the database any information or correction on the subject will be received with much gratitude