Difference between unique index and unique constraints-Oracle
A constraint is defined by Oracle as a declarative way to define a business rule for a column of a table. An integrity constraint is a statement about a table's data that is always true. The difference between a unique index and a unique key/primary key constraint starts with the fact that the constraint is a rule while the index is a database object that is used to provide improved performance in the retrieval of rows from a table. It is a physical object that takes space and is created with the DDL command: create index or as part of a create table with primary key or unique key constraints or an alter table command that adds these constraints (see SQL Manual). Briefly the constraints are: Not Null - Column value must be present. Unique Key - Column(s) value(s) must be unique in table or null (see note below). Primary Key - Unique key + Not Null which equates to every column in the key must have a value and this value is unique so the primary key uniquely identifies each and ev...
Thanks. Exactly what I was looking for.
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