code: private String getSelectClauseFragment(SignatureVariable var,
  										   Term term,
  										   Optional<TermType> termType,
  										   AliasIndex index) {
  		/*
  		 * Datatype for the main column (to which it is cast).
  		 * Beware, it may defer the RDF datatype (the one of the type column).
  		 *
  		 * Why? Because most DBs (if not all) require the result table to have
  		 * one datatype per column. If the sub-queries are producing results of different types,
  		 * them there will be a difference between the type in the main column and the RDF one.
  		 */
  		String typeColumn = getTypeColumnForSELECT(term, index, termType);
  		String langColumn = getLangColumnForSELECT(term, index, termType);
  		String mainColumn = getMainColumnForSELECT(term, index, var.castType);
  
  		return new StringBuffer().append("\n   ")
  				.append(typeColumn).append(" AS ").append(var.columnAliases.get(0)).append(", ")
  				.append(langColumn).append(" AS ").append(var.columnAliases.get(1)).append(", ")
  				.append(mainColumn).append(" AS ").append(var.columnAliases.get(2))
  				.toString();
  	}
docs: produces the select clause of the sql query for the given CQIE
  
  @return the sql select clause