This chapter describes the embedded SQL package
  for PostgreSQL. It was written by
  Linus Tolke (<linus@epact.se>) and Michael Meskes
  (<meskes@postgresql.org>). Originally it was written to work with
  C. It also works with C++, but
  it does not recognize all C++ constructs yet.
 
This documentation is quite incomplete. But since this interface is standardized, additional information can be found in many resources about SQL.