Is SQL is an external language, conceptual language or internal language?

Also, HOw many external schemas can be written for one conceptual schema?

what do you mean by internal or external language?

just guessing its both.

its internal to SQL database engines, its external when using some procedural languages to access the database engine. such procedural languages could include Visual Basic, Visual C/C++, dBase, PL1, VBA, Turbo Pascal, Delphi etc....

depending on how you deffine internal language it may also be external in the database engine. (where for example a user uses SQL queries to extract information directly from the database).

Theoretically it could also conceptual when its used to encapluslate the data model design.