--- In firebird-support@yahoogroups.com, "mariofb123" <mariofb123@...>
wrote:

>
> The table consists of 3 fields: EVENTDATE, EVENTTYPE, EVENTKEY. All 3
> fields are used in the combined primary table index.
> I am trying to delete the EVENTTYPE field, however Firebird does not
> allow for this. How to get rid of this field and change the primary
> index to consist of the two remaing fields only ? I cannot delete and
> recreate the table, as it already contains data.
>
> note: the original command to create the primary index was:
> ALTER TABLE GH ADD PRIMARY KEY (EVENTDATE, EVENTTYPE, EVENTKEY);
>

You will first need to drop any items that depend on the primary key,
such as foreign key constraints if applicable.

You then need to drop the primary key constraint. This is a bit more
tricky because you did not name it when you created it, so it will
have a silly autogenerated name.

SELECT RDB$CONSTRAINT_NAME
FROM RDB$RELATION_CONSTRAINTS
WHERE RDB$RELATION_NAME = 'GH'
AND RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'

That will return to you the name, so you can then use

ALTER TABLE GH DROP CONSTRAINT <from above>;

Then you can redeclare the primary key providing that the new fields
meet the criteria (not null and guaranteed unique for every record).

Just a tip for the future, don't use superkeys as primary keys. Create
a surrogate value that you fill with a generator, and you avoid a lot
of issues.

Adam