The ninth practice

JavaScript programming problem

The difference between null and undefined?

Only one type undefined value, i.e., undefined. When the variable declaration has not been initialized, the default variable is undefined.
only one type of null value, i.e., null. null object has not been used to indicate the presence, used to indicate the function attempts to return an object that does not exist.

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MySQL programming problems

Table students

id	sno	username	course	score
1	1	Joe Smith	Chinese	50
2	1	Joe Smith	mathematics	80
3	1	Joe Smith	English	90
4	2	John Doe	Chinese	70
5	2	John Doe	mathematics	80
6	2	John Doe	English	80
7	3	Wang Wu	Chinese	50
8	3	Wang Wu	English	70
9	4	Zhao six	mathematics	90

Check out only enrolled in a course of all students in school number and name.

SELECT sno,username,count(course) FROM students
GROUP BY sno,username
HAVING count(course) = 1;

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Java programming problem

Print out all the "narcissistic number", the so-called "digital daffodils" refers to a three-digit number, which is equal to the digits of the cube and the number itself. For example: 153 is a "narcissistic number" because cubic cubic 153 cubic 1 = +5 +3.

Package Test; 

/ ** 
 * @author the CUI 
 * 
 * / 
public  class the Test { 

    public  static  void main (String [] args) {
         for ( int NUM = 100; NUM <1000; NUM ++ ) {
             // digit 
            int A = 10% NUM ;
             // tens 
            int B = NUM / 10% 10 ;
             // hundreds digit 
            int C = NUM / 100% 10 ; 

            IF (Math.pow (A,. 3) + Math.pow (B,. 3 ) + Math.pow (C,. 3) == NUM) { 
                System.out.println (NUM);
            }
        }
    }
}