Create Primary Key « Constraints « Oracle PL / SQL

1.Using a CREATE TABLE statement: create a table with primary key
2.Create a foreign key "set null on delete" with more than one field, and use desc to check
3.Violate the primary key and foreign key relation
4.ORA-12991: column is referenced in a multi-column constraint
5.One-to-one using a primary-key and foreign-key relationship
6.Use three columns as primary key
7.Set primary key when declaring a column