Question { IBM, 8583 }

If a table column has is UNIQUE and has NOT NULL, is it
equivalent to a PRIMARY KEY column?

Answer

No. Generally Primary Key contains Unique + NotNull values.
If we are not defined a column as Primay Key and we defined
as Unique + NotNull, then, the behavior of that particular
column in that particular table looks like primary key. but
this cannot be referenced in any other table as we have not
defined as primary key..So, Primary Key column is different
from the column which have Unique + Not Null qualities.

Question { 3274 }

What is Virtual Memory?

Answer

It is a private memory/temporary memory. Actually there will
not be any memory like virual. when u execute any query,
that time it process the query in virual memory, which is
not physical but uses physical memory as virtually. once the
query execution done, we lose virtual memory. dynamically it
creates memory part from physical memory. but not physical.