sql is a declarative language used to manage relative databases easily.Usually it was known as SEQUEL, simple english query language but then the name changed later. The langauge was theoretically given by codd, but was practically implemented by IBM later in 70s.
It has a procedural part too known as plsql where the functions and procedures are allowed.
Also declarative just means declaring what we are going to do and not specifying how to do it unlike the programming languages.