It's good to quickly grasp basic syntax so you can read code in unfamiliar language. However, I don't think that it's a good resource to properly learn language.
You will often miss learning the philosophy of the language (the $language_name way of doing it), the different way of thinking about the problems that the language provides and similar details, which are often not necessary to read a snippet of code, but you want to understand it in order to properly learn the language and make the most of it.
SQL is a good example of it. It might be trivial to explain the syntax of most common SQL queries, but thinking in relations and tables is not natural to most people so there's not much you can do with basic syntax.
You will often miss learning the philosophy of the language (the $language_name way of doing it), the different way of thinking about the problems that the language provides and similar details, which are often not necessary to read a snippet of code, but you want to understand it in order to properly learn the language and make the most of it.
SQL is a good example of it. It might be trivial to explain the syntax of most common SQL queries, but thinking in relations and tables is not natural to most people so there's not much you can do with basic syntax.