question: private Set < String > primaryKeys ( PreparedStatement stmt , String owner , String tbl ) throws SQLException { Set < String > pkCols = new HashSet < > ( ) ; stmt . setString ( 1 , owner ) ; stmt . setString ( 2 , tbl ) ; try ( ResultSet pkRs = stmt . executeQuery ( ) ) { while ( pkRs . next ( ) ) pkCols . add ( pkRs . getString ( 1 ) ) ; } return pkCols ; }
target:  Retrieve primary key columns.