Explain various types of constraints in Oracle.

Answer

Oracle "Check" Constraint:

It validates incoming columns at row insert time.

Not Null Constraint:

It is used to specify that a column may never contain a NULL value.

Primary Key Constraint:

It is used to identify the primary key for a table. This operation requires that the primary columns are unique, and it creates a unique index on the target primary key.

References Constraint:

This is the foreign key constraint and is only applied during INSERT and DELETE.

Unique Constraint:

It is used to ensure that all column values within a table never contain a duplicate entry.