presto-main/src/main/java/io/prestosql/sql/planner/plan/Assignments.java/Assignments/isIdentity
class Assignments:    public boolean isIdentity()
    {
        for (Map.Entry<Symbol, Expression> entry : assignments.entrySet()) {
            Expression expression = entry.getValue();
            Symbol symbol = entry.getKey();
            if (!(expression instanceof SymbolReference && ((SymbolReference) expression).getName().equals(symbol.getName()))) {
                return false;
            }
        }
        return true;
    }