core/SqlSelector.php
public function join(string $sql, $args = null)
    {
        $sql = trim($sql);
        if (!preg_match('@^(left|right|full|outer|inner|join)\s+@', $sql)) {
            $sql = 'join ' . $sql;
        }
        if ($this->joinItem === null) {
            $this->joinItem = new SqlItem($sql, $args);
        } else {
            $this->joinItem->add($sql, $args);
        }
        return $this;
    }
public function join(string $sql, $args = null)
    {
        $sql = trim($sql);
        if (!preg_match('@^(left|right|full|outer|inner|join)\s+@', $sql)) {
            $sql = 'join ' . $sql;
        }
        if ($this->joinItem === null) {
            $this->joinItem = new SqlItem($sql, $args);
        } else {
            $this->joinItem->add($sql, $args);
        }
        return $this;
    }
join
@param string $sql
@param null $args
@return $this