Names of Constraints

User_constraints

there are different type of constraints

1) primary key
2)unique key
3)foreign key
4)check constraints

USER_CONSTRAINTS describes constraint definitions on tables in the current users schema.

there are 5 constraints and they are:-

1.primary key
2.foreign key
3.unique
4.not null
5.check

Select * from user_constraints /// To view the constraints at table level

user-constraints and all_constraints

Constraints divided into 3 types those are:
1. domain integrity constraints:- not null,check
2. entity integrity constraints:- unique,Primary key
3. referential integrity constraints:- foreign key

In these not null used only in column level, (check, unique, primary key) are used in all 3 levels (column,table.alter levels) and foreign key can used in table and alter levels only.