Instr() function on drupal
A plain db_query() might be easier for this particular query, but if you want to use db_select() you can make use of the SelectQuery::where() method:

$string = 'Americana Abstract Art Art Antique Jewelry Antique Jewelry Jewelry';

$query = db_select('cms_tags', 'ct')
  -&gt;fields('ct')
  -&gt;where('INSTR(:string, ct.name)', array(':string' =&gt; $string));