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I used MongoDB for personal projects, but its more of a JS style query language. I only used SQL in school with Java JDBC and C++ Qt other than that
SQL is really important if you work with data and databases. As soon as you want to save some data in a database you need SQL. If you want to retrieve data from a database you need SQL Try to code a library app. Make a books-table. Read the rows from the database, Store new books in the database and give the user the possibility to update book-defintions. In what did you make so far and in what language ? I use it a lot. I use the sql-express as database and sql as querylanguage.
It can also be used in the context of statistical (machine) learning. When you have massive datasets and you'd like to work with a subset of the original dataset, SQL is the way to go.
Sql is a must for developers. If you need to create an application,obviously there must be a database. Even to hack something, you must get access to databases, then you must know sql commands to retrieve information. So Sql is important.
Daniyal mustafa please start a own thread. Your question is not a answer to this question.