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

0 vote115 views1 answer
Sql cheetsheet
SQL
0 vote120 views1 answer
How to check which table has data in mysql
SQL
1 vote110 views1 answer
Mysql find tables with column name
SQL
0 vote110 views1 answer
Ajouter une contrainte de clé étrangère sql
SQL
1 vote121 views1 answer
Postgresql round double precision
SQL
36 votes120 views6 answers
Delete from where sql
SQL
0 vote142 views1 answer
How to add auto increment primary key
SQL
0 vote112 views1 answer
Truncate table sql server foreign key
SQL
0 vote128 views1 answer
Ignore case in string sql
SQL
0 vote112 views1 answer
Python sql last insertend
SQL