AB Rizni If you want to be full stack developer then SQL is necessary. In case of web developer SQL is required when you need to make dynamic website otherwise no need.
Check this code to know more about web developer:-
Html and css both can be use together so we can learn together.
SQL is used in back-end programming. There is no relation with html and css.
If you want to be SQL developer or database analysist then no need to learn html and css.
When you get comfortable with HTML you should learn. When you will learn CSS you will need HTML. It is good to learn one by one. Because when you try to learn everything at same time you will definitely get confused. It will make you things hard.