>Not sure what you want to do. Are you trying to insert a new record and check if the key already exist? If so, you are going into trouble in a multiuser/multisession environment. Better to use an auto-increment integer field, a GUID or a reference table for that.
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>>How to check if one key already exists using indexseek. I know that indexseek does not consider the current record when I am inserting, but when the record is not new the indexseek check the current record too.

I have one table with one column that is defined with primary key. In this table I have a second column that could be defined with candidate index, but it can not because this column admit no value for that. But if the second column have one value this value must be unique.

I would like to check the unique value for the second column with indexseek. When I am inserting a new record no problem, but when I am updating one record the indexseek validate against the current record too, and it says that the record already exists.