Primary key can be assigned to only 1 column in the table but this is not

WHAT IS THE DIFFERENCE BETWEEN PRIMARY KEY(PK) CONSTRAINT
AND UNIQUE KEY(UK) + NOT NULL(NN) CONSTRAINT ASSIGN TO A
COLUMN ?
INSTEAD OF ASSIGNING PK ,WE CAN ASSIGN UK + NN TO A COLUMN.
WHAT ARE THE MARRITS AND DEMARITS BETWEEN THE ABOVE TWO?THE
ABOVE TWO ARE SAME,THEY DON'T ALLOW DUPLICATE AS WELL AS
NULL VALUES.

Question Posted / shwetalguglanicse

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Answer Posted / shwetalguglanicse

Primary key can be assigned to only 1 column in the table but
this is not with unique key
And UK allow duplicate value but PK does not .

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