What is the difference b/w Primary Key and Unique Key

Question

I tried to find it out in google but not satisfactory answer is given out there. Can anybody explain the solid difference.

actually if Primary key is used to sele

Answer 1

NOT NULL means Any entry in that particular column should not be null. UNIQUE means Each entry in the column should be distinct. PRIMARY KEY means Any entry in the column should be distinct and not null.

So simply..

  PRIMARY KEY= UNIQUE + NOT NULL