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2 votes
E No Ename DeptNo
E001 A 10
E002 B 10
E003 B 5
E004 C 10
E005 D 20
E001 A 20
E003 B 10

So , if I do the first query 

it will give 

ENo
E001
E002
E004
E003

Union

ENo
E005
E002

so, Union will remove duplicate entries.(i,e E002)

ENo
E005
E002
E001
E004
E003

But if we do the second query , we will get the duplicate tuples.

So, option (b) is true , Q1 is subset of Q2

 

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