An ORM is not a high-level version of SQL though. A more accurate metaphor for an ORM would be like a converter from one high level programming language that is object oriented, to another high level programming language that is functional.
In the case of C#, LINQ is a declarative built in part of the language. At runtime, it is converted into an AST and if you use Entity Framework, it is translated into SQL - another declarative language.
You can theoretically express any standard SQL query in LINQ even though outer joins can be obtuse at first. The translation may not be as optimal as hand written sql, but no compiler can translate code into assembly that would be as optimized as someone who could hand roll their own. We decided decades ago that high level languages were worth the trade off most of the time.
