Zend Db - WHERE clauses with OR

<?php

    $searchConditions      = array();

    $searchConditions[]    = $db->quoteInto ('a.field1 IN (?)', $array );
    $searchConditions[]    = $db->quoteInto ("a.field2 LIKE '?%'", $input, 'INTEGER' );

    $select->where (new Zend_Db_Expr(implode(' OR ', $searchConditions)));