It updates an existing index of the same tagname. If the tagname does not exist, it adds it to the CDX. If you have several index TAGs, all of them will be in a single CDX file. Open a table that has several of these tags, and do a DISPLAY STATUS. You will see all the index keys and tags.

>Mark,
>
>That just updates the existing index and doesn't add other, correct?
>
>>>I need to change and index expression from a table from the default (field name) to VAL(fieldname). I can do this easily in the Project Manager, but I need to do this on an installed site using commands in an update program.
>>>
>>>I thought I would use an ALTER TABLE command but do I need to DROP the FOREIGN key first (it's a 'regular' key) and then ADD the new key? What would the commands be>
>>>
>>>
>>>Thanks
>>
>>Since it is a regular key, there is nothing to drop, open the table exclusively and issue the command:
>>
>>INDEX ON VAL(fieldname) TAG tagname