unique key

Mathew_paul · #1 (**permalink**) 12-30-09, 07:54

hi

unique key won,t allow null values
more than one unique key can be created in a table
unique key won,t allow duplicate values
unique key default creates a indexe

What is the major difference unique and primary key ??

regds
Paul

r937 · #2 (**permalink**) 12-30-09, 08:14

Quote:

Originally Posted by Mathew_paul

unique key won,t allow null values

are you sure?

tonkuma · #3 (**permalink**) 12-30-09, 09:48

Quote:

Originally Posted by Mathew_paul
unique key won,t allow null values

are you sure?

Yes, unique constraint don't allow null values.
unique constraint and unique index are different things.

Descriptions of UNIQUE (column-name,...) and PRIMARY KEY (column-name,...)
in TABLE statement in "DB2 SQL Reference" are essentialy same, except...

Quote:

Only one primary key can be defined on a table.

Another use of PRIMARY KEY is...

Quote:

REFERENCES table-name or nickname

.....
.....

(column-name,...)

.....
.....

The list of column names must match the set of columns (in any
order) of the primary key or a unique constraint that exists on T2
(SQLSTATE 42890). If a column name list is not specified, then T2
must have a primary key (SQLSTATE 42888). Omission of the
column name list is an implicit specification of the columns of that
primary key in the sequence originally specified.

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