Null records inserted

Hello.

I have a PostgreSQL (V7.0.2) database with several tables defined with
a primary key set by default to a sequence value.

99% of the time this works as expected but there is a trickle of
records appearing in each table where every field is null.

Could somebody please explain to me how this is possible so that I
might be able to track down the programming error that causes them.

That is, how can a field that is defined as having a default value wind
up in the database as null.

Despite the usual rules regarding null processing, I would still expect
a second unique primary key value of null to be rejected.

The database is usually maintained via a VB5 ODBC application.

Cheers and thanks,
Stephen Davies

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Stephen Davies Consulting scldad(at)sdc(dot)com(dot)au
Adelaide, South Australia. Voice: 08-8177 1595
Computing & Network solutions. Fax: 08-8177 0133