Unique vs primary key

What is the difference between UNIQUE and PRIMARY KEY constraints? 
There should be only one PRIMARY KEY 
in a table whereas there can be
any number of UNIQUE Keys.
PRIMARY KEY doesn’t allow NULL
values whereas Unique key allows NULL values.

Similar codes

7 votes372 views2 answers
Phpmyadmin change password
SQL
3 votes338 views1 answer
Oracle function
SQL
3 votes365 views1 answer
Get current month last date in sql server
SQL
0 vote362 views1 answer
Clear query cache sql server
SQL
0 vote339 views1 answer
Aktor yang pernah terlibat di film bergenre Aksi di sql
SQL
0 vote384 views1 answer
SQL FROM-Klausel
SQL
0 vote361 views1 answer
Drop specific row postgresql
SQL
0 vote352 views1 answer
Vowels in sql
SQL
0 vote341 views1 answer
Oracle enable chain
SQL
0 vote345 views2 answers
Postgres another version
SQL