Virtual Gate Test Series: Databases - Sql query

Question

Consider the following instance R.

A	1	2	3	4
B	Null	1	2	2

The number of tuples returned by the following SQL query is _____________.
> select * from R as R1
   where not exists (select * from R)  where B = R1.A                          

Comments

yes undefined ....

let comparison is like this....

any Number =NULL (here we r not sure about the value of NULL therefor False)

Number>NULL(again we r not sure about the value of NULL therefor False)

Number<NULL(again we r not sure about the value of NULL therefor False).....

therefor we say that the comparison with NULL gives undefine ...

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Then NOT exist (undefined) will not return any rows

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I think the answer should be 2 as the two tuples with A as 3 and 4 should be returned as they do not have an equivalent value in B.

Answer 1

there is a mistake in parathezisation...it will be 2