Compose Where Clause for Searching

<?php
/**
 * @param $query The string you wish to search for
 * @param array database columns to include in search
 * @return string SQL where clause
 */
public function createWhereClause($query, array $fields)
{
    $words = explode(' ', $query);
    foreach ($fields as $field)
        foreach ($words as $word)
        {
            if (isset($whereClause) && strlen($whereClause) > 0)
                $whereClause .= ! isset($currentField) || $field == $currentField ? " AND $field LIKE \"%$word%\"" : ") OR ($field LIKE \"%$word%\"";
            else
                $whereClause = "WHERE ($field LIKE \"%$word%\"";
            $currentField = $field;
        }
    return "$whereClause)";
}

/**
 * createWhereClause('niels', ['username', 'email']); = WHERE (username LIKE "%niels%") OR (email LIKE "%niels%")
 * createWhereClause('niels faurskov', ['username', 'email']); = WHERE (username LIKE "%niels%" AND username LIKE "%faurskov%") OR (email LIKE "%niels%" AND email LIKE "%faurskov%")
 * createWhereClause('niels fau', ['username', 'email','fullname']); = WHERE (username LIKE "%niels%" AND username LIKE "%fau%") OR (email LIKE "%niels%" AND email LIKE "%fau%") OR (fullname LIKE "%niels%" AND fullname LIKE "%fau%")
 */