How to give a field a default value

[JimR]

odd ask I know but how ever here it is
I want to add a default value to a thread field by way of a database query
an example

PHP Code:

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$select=$db->query("select * from ".TABLE_PREFIX."threadfields_data where tid ='".$post['tid']."'"); $num_rows = $db->num_rows($select); //rows for the record only 1 or 0 // if no row format the address switch ($num_rows){ case 0: // no record add the default address to the collection address fields $GLOBALS['threadfields']['add1']['value'] == $sub.$build; break; case 1: // do nothing break; }

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the variables $sub & $build have already been defined and need to become the default.
Currently I am inculding a php file within the template which defines my variables however with this I get parse errors am I putting the code in the wrong place ... does it need to be placed in a plugin that calls a hook before xthreads ?