UNIQUE index vs. PRIMARY KEY constraint to rebuild Oracle indexes and constraints

An Oracle user asks whether it's redundant to use both a UNIQUE index and a PRIMARY KEY constraint to rebuild Oracle indexes and constraints on a very large table.

I am rebuilding indexes and constraints on a very large table and need to accomplish this as fast as possible.

If I create a UNIQUE index on this table (4 concatenated not null columns) AND use the alter table command to enforce...

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the primary key, is this totally redundant?

Here are the statements I'm using and the elapsed time it is taking.

1) Create unique index X on X nologging (53 minutes).

2) Alter table X add constraint X primary key (col1, col2, col3) using index (one hour 50 minutes).

Technically, a UNIQUE index and a PRIMARY KEY constraint are a little different. Both enforce uniqueness, but the PK constraint also ensures that all values in the columns cannot be NULL. But to cut down on the time, I would just perform one statement, the ALTER TABLE ADD CONSTRAINT command. This will build the index and enable the constraint in one operation.

This was last published in December 2008

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