As a web developer If I just know how to deal with mysql , do I need to learn oracle or MS SQL or postgresql ? observe that facebook use mysql.

Hi friend,

In order to be an efficient developer you should lear staff from begining, so Mysql's bases learning is great to know the differente interaction and reuires in your developer carreer.

you not need to learn other language

mysql suffisant

 I agree with the answer given by nassreddine seydi   Web and Hybrid Mobile apps Developer.