  specifies a table constraint whose name, table name, and schema name
     should be included as auxiliary fields in the error report.  Indexes
     should be considered to be constraints for this purpose, whether or
     not they have an associated <code class="structname">pg_constraint</code> entry.  Be
     careful to pass the underlying heap relation, not the index itself, as
     <code class="literal">rel</code>.
    </p></li><li class="listitem"><p>
     <code class="function">errdatatype(Oid datatyp