core/SqlSelector.php
public function joinOn(string $sql, $args = null)
    {
        $sql = trim($sql);
        if ($this->joinItem == null) {
            return $this;
        }
        $sql = 'on ' . $sql;
        $this->joinItem->add($sql, $args);
        return $this;
    }
public function joinOn(string $sql, $args = null)
    {
        $sql = trim($sql);
        if ($this->joinItem == null) {
            return $this;
        }
        $sql = 'on ' . $sql;
        $this->joinItem->add($sql, $args);
        return $this;
    }
Join ON 条件
@param string $sql
@param null $args
@return $this