SQL_IN_Query

Question

Answer should be $0$ row,right?

Comments

here i meant implementation of a unique key with  not null when we dont declare a primary key for a table as either we have to declare a key as primary key or we can manage it by declaring unique not null.

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for a table to exist uniquely there must be a primary key so as to prevent the wastage of space to be more precise.

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that what i am saying also.... even though you declare PK, UK + NOT NULL internally declared as PK

to prevent the wastage of space to be more precise

The space required for declaring UK and PK is equal 

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here i have not compared memory for uk and pk...

i have told about why we need to identify records uniquely either by uk or by pk.

Answer 1

yes Given answer is Wrong ..it should return 0 rows..

In database the NULL is Undefined or Unknown .. so one Null can never be equal to another NULL ..

So as there is no matching .. it will simply return 0 rows...Definately it will compare NULL with NULL ...

but as they are unknown we can say nothing ...as a result compiler will simply return 0 rows

Answer 2

comparing null with null gives you error in mySql.

Comments

NULL when compared to null gives Null in SQL.