class_docstr: A `Composable` representing a snippet of SQL statement.
  
  `!SQL` exposes `join()` and `format()` methods useful to create a template
  where to merge variable parts of a query (for instance field or table
  names).
  
  The *string* doesn't undergo any form of escaping, so it is not suitable to
  represent variable identifiers or values: you should only use it to pass
  constant strings representing templates or snippets of SQL statements; use
  other objects such as `Identifier` or `Literal` to represent variable
  parts.
  
  Example::
  
      >>> query = sql.SQL("select {0} from {1}").format(
      ...    sql.SQL(', ').join([sql.Identifier('foo'), sql.Identifier('bar')]),
      ...    sql.Identifier('table'))
      >>> print(query.as_string(conn))
      select "foo", "bar" from "table"
code: def as_string(self, context):
      return self._wrapped
  
imports: import string
  from psycopg2 import extensions
label_desc: Use image node_id 3 for calling the SQL obj's underlying member method code with example usage: obj.as_string(context) and returns: self