学习JDBC的一些事(关于学习过程中出现的一些错误)

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: 
　　You have an error in your SQL syntax; 
　　check the manual that corresponds to your MySQL server version for the right syntax to use near 
　　‘WHERE idcard=‘123412199507082314‘‘ at line 1

private Student searchStudent(int searchType) {
        String sql="SELECT flowid,type,idcard,examCard,studentName"
                + ",location,grade"
                + "FROM examstudent "
                + "WHERE ";
        
        Scanner scanner=new Scanner(System.in);
//        1.根据输入的searchType确定查询的方式
//        2.根据searchType确定sql语句
        if(searchType==1){
            System.out.print("请输入身份证号：");
            String idCard=scanner.next();
            sql=sql+"idcard=‘"+idCard+"‘";
        }else{
            System.out.print("请输入准考证号：");
            String examCard=scanner.next();
            sql=sql+"examCard=‘"+examCard+"‘";
        }