code: public static String getColumnSharedPrefix(String[] associationKeyColumns) {
  		String prefix = null;
  		for ( String column : associationKeyColumns ) {
  			String newPrefix = getPrefix( column );
  			if ( prefix == null ) { // first iteration
  				prefix = newPrefix;
  				if ( prefix == null ) { // no prefix, quit
  					break;
  				}
  			}
  			else { // subsequent iterations
  				if ( ! equals( prefix, newPrefix ) ) { // different prefixes
  					prefix = null;
  					break;
  				}
  			}
  		}
  		return prefix;
  	}
docs: Returns the shared prefix of these columns. Null otherwise.
  
  @param associationKeyColumns the columns sharing a prefix
  @return the shared prefix of these columns. {@code null} otherwise.