I have heard a couple of variations of these analogies. I do not like them. I think they are simply absurd.
At last PDC, “M” was to “SQL” what C is to Assembler. This year it was, what VB is to C. And now I even read this:
The code name “M” language is like a more manageable (though more limited) form of Transact-SQL, the language normally used to describe data schema and values.
Kraig Blockschmidt, Microsoft Data Development Technologies: Past, Present, and Future
“M” has some overlaps with T-SQL, ok. But far from every concept in “M” can be translated into T-SQL. What about structural subtyping? Types without identities? Polymorphic references and function arguments? Languages/DSLs? Ordered collections? Lot’s more.
And only a very small, although useful subset of T-SQL maps to “M”. Also most of the translation to SQL is opinionated, not natural.
What the schema and values part of M compares much more to, is XML and XSD.
Would you even try to compare XML to T-SQL?