Self Doubt : SQL

Question

HI

Why it is necessary to assume ? why do we nned that line ?

Answer 1

Option D would be correct. 

Now if the statement  " Each of the Employee makes sale to at least one customer " is removed then their might exist an employee who does not have made any sale (suppose E1) and as E1 has not made any sale it would not be present in SalesRepID (FK referring to Empid in Employee Table) in Customer Table.

Now if the above query is run on such case then E1 would be selected (Internal Query will return NULL for E1) along with other Valid Employee Names who have good Rating with all their customers even though E1 has not made any sale.   

Comments

yaa, now got it. thnx

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@daksirp

if you got it from his answer, then select it as BEST