Question

Multiple choice

Consider the following ORACLE relations :
One (x, y) = {<2, 5>, <1, 6>, <1, 6>, <1, 6>, <4, 8>, <4, 8>}
Two (x, y) = {<2, 55>, <1, 1>, <4, 4>, <1, 6>, <4, 8>, <4, 8>, <9, 9>, <1, 6>}

Consider the following two SQL queries SQ1 and SQ2 :

SQ1 : SELECT * FROM One)            
          EXCEPT            
         (SELECT * FROM Two);
  
SQ2 : SELECT * FROM One)            
          EXCEPT ALL           
         (SELECT * FROM Two);

		2 and 2 respectively
		1 and 2 respectively
		1 and 1 respectively
		2 and 1 respectively

Answer 1

Answer: 1 and 2 respectively.

• SQ1 : SELECT * FROM One)            
            EXCEPT            
           (SELECT * FROM Two); It eliminates the duplicate values. 

• It's generally  {<2, 5>, <1, 6>, <1, 6>, <1, 6>, <4, 8>, <4, 8>} -  {<2, 55>, <1, 1>, <4, 4>, <1, 6>, <4, 8>, <4, 8>, <9, 9>, <1, 6>}
• <1,6> and <4,8> Were there in the second set, so remove all occurances of them in the first set. So you will get {<2,5>} , which is only one element.

• SQ2 : SELECT * FROM One)            
            EXCEPT ALL           
           (SELECT * FROM Two); It does not eliminate duplicate values, it keepes them as it is.

• It's generally  {<2, 5>, <1, 6>, <1, 6>, <1, 6>, <4, 8>, <4, 8>} -  {<2, 55>, <1, 1>, <4, 4>, <1, 6>, <4, 8>, <4, 8>, <9, 9>, <1, 6>}
• In the second set <4,8> present twice. So you can remove <4,8> , <4,8> (both) from the first set.
• In the second set we have only two <1,6>. But in our one set we have three <1,6>. So we can remove two of them and one <1,6> will remain there.
• So the result will be {<2,5>,<1,6>}, in which 2 elements are present.