SQL & PL/SQL

A primary key in Oracle has to be on not null-columns. A unique key in Oracle can have null values.

However you can't create a unique or primary key on a nclob-column. You can use a varchar2(4000)-column, 4000 is the max length of a varchar2-column.

If you are certain that the PRIMARY INDEX in Teradata can have duplicates then you can't use a UNIQUE index/constraint in Oracle because it's supposed to be unique as the name suggests (although it can have an arbitrary number of nulls in contrast to the PRIMARY KEY which is NOT NULL by definition).

In that case you would end up with an conventional index in Oracle, which can have duplicates (and normally doesn't index NULL values).

Note that you can define the UNIQUE CONSTRAINT to be deferred in Oracle which means that it temporarily can hold duplicates (until you COMMIT or issue SET CONSTRAINTS) but I doubt that this is what you're looking for.

In addition you need to be aware of index key length limits on Oracle, which are based on the block size of the tablespace where the index is stored. Only if you use at least a blocksize of 8k you're able to create an index on a VARCHAR2(4000) column, otherwise it will fail with an error. The maximum key length in an 8k tablespace in Oracle 10g is approx. 6k I think (e.g. in case of a composite index created on multiple columns).

Regards,
Randolf

Oracle related stuff blog:
http://oracle-randolf.blogspot.com/

SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/

Hello Randolf:

I appreciate your input.

A PRIMARY INDEX in Teradata can have duplicates and nulls so it looks like I would be looking at a conventional index.

Can this be created when you create the table DDL or is the correct way to do it to use a separate CREATE INDEX statement?

CREATE INDEX <index> on <table> (column 1, ..., column n);

I couldn't really find in the documentation how to create an index in the DDL although it could be there. The CREATE TABLE statement syntax was about 15 pages so I might have missed it! ;)

Thansk for your help.

Thanks for your help. I found this in the documentation also so I'll need to check the data types I'm converting to before creating any kind of primary key.

None of the columns in the primary key can be LOB, LONG, LONG RAW, VARRAY,
NESTED TABLE, BFILE, REF, TIMESTAMP WITH TIME ZONE, or user-defined type.
However, the primary key can contain a column of TIMESTAMP WITH LOCAL
TIME ZONE

Conventional indexes that are not used to enforce a unique or primary key constraint can only be created using a separate CREATE INDEX command.

Indexes that are used to enforce a unique/primary key constraint can and will be part of the CREATE TABLE command, and starting with Oracle 9i you can even use an explicit CREATE INDEX statement as part of the USING INDEX clause that is optionally part of the "constraint" definition.

And there is of course another special case: If you create a so called index-organized table which is actually an index used as a table then of course you're implicitly creating an index because it represents the table :-)

Regards,
Randolf

Oracle related stuff blog:
http://oracle-randolf.blogspot.com/

SQLTools++ for Oracle (Open source Oracle GUI for Windows):
http://www.sqltools-plusplus.org:7676/
http://sourceforge.net/projects/sqlt-pp/